I decided to check out the save file and learned a few things:

1, Scrolls are random at higher levels. It seems there is a limit to the number that can be in stock at any one time. It is possible for weak spells to show up at higher levels. I didn't see anything like Mass Regeneration or Comets Shower, however. Incinerate Air and End of Flames always restock to a quantity of 2, however. (I saw End of Flames I show up randomly, which appears to be the same as End of Flames, but more expensive.)

2. Weaker potions eventually disappear from the store. No more Potion I/II at high levels. (You can still get Light Heal V scrolls if you really want them, however.)

3, The store restocks at 10 am, right when the day advances. For the first town, the restocks are on the multiple-of-3 days. One possible strategy might be to save right before 10 am and then reload if the item you want doesn't appear.

4. Training costs (on Normal difficulty): starts at 50, increase by 50 the first 9 trainings, then increase by 1000 up to 19-20 trainings (cost about 1500). After that, no more, but the trainer says something about being trained in other villages.

5. Inn costs do not scale. Therefore, if you are in town and need to rest, going to the inn makes sense at higher levels. Note that (on Normal difficulty) this is not the case at lower levels: If you can get a day's food for less than 60 gp, you should buy the food from the merchant and rest instead. (Remember, resting at the inn does not cost any food.) If you want to restock the items quickly, 3 days of rest costs only 120 gp in total.

In such situations you just reload. On higher difficulty modes each scroll directly translates to X cycles of cereal farming. Reload takes less time, trust me.
It will be available to you very very soon. Sacrificing power in long run might work on first difficulty mode, but on 2nd+ difficulty modes you will dearly regret not maximizing these benefits because enemies will have so much HP in comparison to your damage output, it will be very-very tedious. Don't forget that bonus levels = more HP/PP/Main Stats: thus, efficiency. They will also yield much more skill points than you spend on Learning, if you will start stacking EXP bonuses as early as possible, so you can then actually put points in class skills, and not only in weapon skills, to not fall much behind in terms of hit chance. I think I wrote already, I didn't raise bows on my Bard for 4-5 levels (lack of skill points), so he can't shoot anything at all. Gaulen also started to fall behind (thanks to Herbs and Terrains skills).
Potions and scrolls could help somewhat, but you get so much LESS gold, and blessings are basically required, you simply have no gold for anything else. Basically, cereals are your main gold source at start of the game, and I'll tell you, farming them becomes very boring very very fast, so you'd rather keep reloading tough fights for better RNG outcome than spend another 1-2 cereal cycles to buy 1 scroll. I don't want to try Hardcore, because real difficulty is "old-school veteran" and I tend to always choose "normal" "intended difficulty". But monsters and chests on Hardcore drop even less Gold, and blessings/training cost even more...

Also don't forget that vendor is the only "reliable" source of gear. Front row with bad gear won't go far, so you will need to buy some stuff for them. Btw, I am still seeking way to efficiently reroll RNG on vendor. It will be of especially high importance at higher levels, as vendor will have way too big range of tiers available.
What concerns hoarding potions - it is mostly magic potions/elixirs which are worth keeping. Healing potions are the most useless because they can be used only on their user, thus they can be sold outright.

Seeing you talk about the game makes me not want to play it anymore. I hate it when you have to strictly stick to guides to be able to beat a game rather than just raising stats you feel like and always take whatever you get the first try.

You can play it without much problems on 1st difficulty mode ("Normal"). It is just the higher difficulty modes, which don't give you much freedom in how to develop your chars.

The only thing which can truly screw you on 1st difficulty mode is not investing into Knowledge of Terrains.

Edit: Also you can try out my infinite random encounters mod, partially implemented for some areas. Root of all problems in this and similar games - no respawns. If there is enough interest, I might just make global infinite random encounters mod within this week, as imo killing monsters is more fun than farming cereals and gives more freedom to character development.

This sort of thing is actually why I am playing the game on Normal. (Plus, there's the fact that the difficulty of Elminage Gothic's postgame was becoming a little unreasonable.)

Also, how much Knowledge of Terrains do you actually need? Is 10 enough? 5?

I remember old normal mode(current Old-School Vet) was highly criticized for being way too difficult in all the wrong ways, thus difficulty modes were renamed. I was thinking of following easy fixes, which could make game less frustrating:
1. Static prices for everything. 10 Gold per blessing. 100 Gold to remove curse. 60 Gold for 6 days of food (10 gold per day). Make Torch spell available at Lv.1 (baseline for Gaulen or mage).
2. RNG re-randomizer. Change vendor's assortment by reloading game. Give warning about hounds in time and not when they already started going after you. Change contents of chest by reloading (it partially works, but only when container is deep in fog of war).
3. 3 stat points and 6 skill points per level up, as melee attackers need 3 stats on proper level or they become crippled. (Learning) + (Weapon Skill) + (Class Defining Abilities) average at 6 skill points, hence I think 6 is good number. It still doesn't allow versatility, but it isn't as grim as 4 skill points.

Thus you get same challenge on start of game, late game becomes less tedious, and you don't have to farm cereals unless you really want it.

Pts 1 and 3 are easy to mod in. I need to look closer into game files to see what can be done with vendors.
The more the better, upto max. Time in couple specific zones runs rapidly fast and you take starvation damage in one of those zones even on easiest difficulty. You also get benefits from this skill in most of other zones, as it slows time flow (unless it is already at 100%, can't go slower than that iirc).

That warning in DLC is quite useless. It comes off quite a time after you triggered hounds. Easy way to check - save a bit before getting this warning. Now whatever you do, you will always get the warning shortly after reload and you will always be caught by wolves at less or more same amount of steps after reload. There is no way to properly avoid and prepare for this encounter if you have saved in such situation.
I agree on Learning. In games with finite source of EXP such skills are pretty much mandatory.

Knowledge of Herbs/Terrains make game a bit more varied, but they definitely don't work well without respawnable source of EXP. I am not really sure if food consumption during travel is really a necessity. Food can be consumed only while crossing zones and sleeping. Knowledge of Terrains would still be important (time flies fast, buffs wear off too fast in the desert. etc.) but not to the point of being mandatory skill.

In the case of Knowledge of Herbs, I think it would work better if Herbs would respawn. Alternatively, keep track of the amount of herbs picked at each spot, and make it so that if your come back with more skill, you can get a little more from the spots you previously harvested. This way, the optimal long term strategy would no longer be to avoid harvesting herbs until later.

Also, is the desert some place I can reasonably reach at this point in the game without going into dungeons or fighting unreasonably difficult enemies?

By the way, I decided to try fighting one of those Imps. 2800 HP and hit for like 143 points of damage. I don't think I am ready (but at least that fight had awesome music).

One more question: Could you check how much the weakest healing potion (the one that restores 20 HP) costs on Veteran mode?

Respawnable herbs directly increase stats and resistances, which would make them way too powerful if they'd respawn. Making Alchemy out of Herbs skill with possibility to make potions form herbs, it would be more interesting imo.
Iirc this desert is guarded by tough elemental whom you can't beat without story specific item which you'll get later on.
Those elementals have 4000 HP and hit for 154 (no variance) damage on Old-School Veteran. It is better to kill them though, as they drop a bunch of stat-increasing herbs. Away with their riddles :))
Common item cost doesn't seem to differ (except for lockpicks, torches and crystals). 20 Gold. Screenshot applied for other potions.

Here is my idea: at 1 skill you get 1 unit from herbs, while at 30 skill you get 5, right? What I am thinking is that, if you harvest at 1 skill you would get 1 unit. Then, once you return at 30 skill, you would get 4 more from the same spot, so you will have earned a total of 5. This would still keep herbs limited.

Respawning herbs could work if the game had a bonus dungeon with powerful enemies. Have the herbs guarded by powerful monsters that respawn.

Another thought: What if Knowledge of Herbs had only 5 levels, but each level after the first cost, say, 7 skill points? This would allow the removal of the random factor from herb harvesting without the skill having useless levels. (It would also allow the skill to be maxed out much sooner, but at great cost.)

Also, did you mean to post a screenshot to your last post, because I don't see one?

Too much convoluted decisions, where simple enemy respawn would suffice.

Btw, there was rumor that Numantian games consider adding some optional and probably random dungeon stuff to LoX, which might be respawnable (about respawns it is merely my own assumption).
Yes, I added it half-minute later after making post...

Looking at the save, there is another possible money making strategy:

1. Early in the game, buy some crystals for 100 gold each.
2. Much later, after maxing out Mercantalism, sell the crystals for 194 gold each.

Since the price increases at higher levels, the sell price also increases.

I'm wondering how well this works on higher difficulties. If the price scales faster, it might actually work better.

Torches, lockpicks, shurikens and crystala are subject to different price scaling mechanics. The more of them you buy, the more expensive they become, till a specific cap. So they are rather gold holes...

I tested on my normal save file, and buying out the shop's inventory and resting 3 days did not result in higher prices.

(Unfortunately, I saved on a day number congruent to 3 modulo 0 so I had to rest 3 days, but fortunately, I had enough food.)