When it comes to spending Gaulen's skill points, here is how the math works out.

I am going to consider two main builds: Long-Term (LT) and Short-Term (ST). The difference is that Long-Term maxes out Knowledge of Herbs (KH) and Learning (L); the Short-Term build ignores those skills.

The skills I consider essential are $WEAPON (W), Knowledge of Terrain(KT), and Envenomed Strike (ES). LT adds the other skills I mentioned to the list.

It is assumed that no skill books are found.

For Short-Term, it looks like this:
Level 2: W (2SP), +2SP (2)
Level 3: W (2), KT (2), 0 (2)
Level 4-9: W (2). KT (1), +1 (8)
Level 10: W (2), KT (1), ES (3), -2 (6)
Level 11-19: W (2), KT (1), ES (2), -1 (-3)
Level 20-30: W (2), KT (1), +3 (6)

In other words, for the Short-Term build, you need 3 extra skill points to have the important skills maxed out as soon as possible. This is easy to get (and any extra can be spent on other useful skills, like Perception, Mercantalism, Immunity or thief skills.

For Long-Term, it looks like this:
Level 2: W (2) KH (1) +1 (1)
Level 3: W (2) KT (2) KH (1) -1 (0)
Level 4-7: W 2 KT 1 KH 1 0 (0)
Level 8: W 2 KT 1 KH 1 L 3 -3 (-3)
Level 9: W 2 KT 1 KH 1 L 2 -2 (-5)
Level 10: W 2 KT 1 KH 1 L 2 ES 3 -5 (-10)
Level 11-19: W 2 KT 1 KH 1 L 2 ES 2 -4 (-46)
Level 20-30: W 2 KT 1 KH 1 L 2 -2 (-68)
Level 31-32: KT 1 L 2 +1 (-67)

As you can see, for the Long-Term build, you need 68 extra points to max the important skills. This is *not* easy to get, especially on Hardcore (where skill points are more expensive) without the Talisman. Even on Normal with the Talisman, I don't see this happening unless you deliberately delay leveling up to get more Talisman energy, and doing so delays the aquisition of Learning (costing you EXP in the long run).

Here are thoughts on each skill in terms of conserving skill points:
$WEAPON: You can get away with fewer points in this skill by going with Short Swords, which give a nice +10 Attack bonus. If you really want wounding, you can use Axes rather than Battle Axes. (There's also Short Bows, but they are rather poor at wounding.)
Knowledge of Terrain: I don't know how fast the desert eats food, so I don't know how much of this skill is required. Leveling this skill only up to that point could be an option. (Any ideas of what we're looking at here?)
Knowledge of Herbs: An optimal long-term strategy avoids gathering herbs until this skill is maxed out. Sacrificing a point here and there will delay it, but not weaken you in the long run.
Learning: If you are willing to sacrifice a bit of long-term power, you could put fewer points into this skill, but note that the sooner you put points into it, the better.
Envenomed Strike: One good reason to not max this skill right away is PP cost. The idea is to decide how many uses you want (maybe 4 on Normal and 3 on harder difficulties, or perhaps 5 and 4 if you want to save some more skill points) and not level up the skill if the cost increase would decrease the number of times you can use the skill. This can free up skill points while keeping ES viable. (The skill is more efficient at higher levels, but that doesn't matter if you have lots of PP you can't use because the skill is too expensive.) Remember, you can level up the skill later and the skill caps at only level 10.

Not a single point in Armors?

Problem with short term plan is that you will end up significantly weaker. That 400% bonus to amount of herbs acquired means TONS and TONS and TONS of stats lost.

Also with Learning your characters would end at 15+ higher levels (note that it works very well with Mercantilism and sacrificing items when you maxed both these skills), which means 60+ more skill points and another big chunk of Stat Points and HP/PP for all the bonus levels.

Quick show:
Need 10 herbs per 1 stat. There are a total of 1018 spawns for herbs in game. Without Knowledge of herbs you get 101.8 Stat Points, 16.9(6) per char. With Maxed skill you get 509 Stat Points, 84.8(3) per char.

84.8(3) - 16.9(6) = 67,8(6)

Which equals skipping 34 levels worth of stat points for everyone! Difference is GIGANTIC.

Maxing Learning will also mathematically give you at very least 10 more levels (more of them, the longer you play). That is trade off 20 skill points for 20 Stat Points AND sizeable HP/PP chunk. It works with sacrificing items, which gives MUCH bigger return if you wait to sacrifice until Learning (and Mercantilism) is maxed.

Hence why I recommend to see Old-School Veteran mode, where stats actually matter. E.g., getting 2-shotted by low level meanies will quickly show you importance of Armor, while expansive HP pools of later enemies will show you what does it mean to throw away hundreds of bonus Stat Points. There is a lot of rough terrain in other places (desert is just being especially nasty). Knowledge of Terrain allows for much higher efficiency unless you really really like to farm food (it becomes old quick enough). You can simply buy tons of mana potions and healing stuff and heal through starvation damage, disregarding Knowledge of Terrain skill altogether. But it will be very expensive, and overall experience will be horrible.

For comfortable gameplay it should be maxed.

Found German video with that desert - watch first few minutes, when Gaulen enters Pernitia, to get rough idea (don't watch more, tons of spoilers). Character has 23 Knowledge of Terrains, and food still disappears extremely fast.

I haven't really found enough armor for Armors to be really important, especially since Strength increases armor capacity.
You mention the long-term benefits of maxing Learning and Knowledge of Herbs, but from what I have read, it is the early game that is difficult, and my Short-Term setup has a lot more skill points to spend on important skills early on. Also, note that there is no longer a reason to delay harvesting herbs, so while you don't get as many stat points, you get them earlier when they are more important.

The German video of the desert is not something I'm interested in watching. I don't like gameplay videos with audio commentary (especially when it's a man speaking), and I *especially* don't like it when the commentary is in a foreign language. (Also, it isn't stated how high Knowledge of Terrain is in that video.)

As a side note: are there any targeted experience rewards? In other words, are there any EXP rewards that I can choose who to give them too (and, in particular, are *not* spread out between party members)?

While game isn't as difficult in its 2nd part, enemies definitely get a LOT of HP (especially on 2nd and 3rd difficulty modes), and some of them can even summon other mobs (no exp from summoned monsters, developers thought of everything), so fights will take quite a time... you don't have to know german or listen to commentator, food consumption is shown in first few minutes of video. Later in this video Gaulen gets a level-up, and commentator increases some skills, including Knowledge of terrains form 23 to 24. Arena, though it is of a limited value (once you won all fights, it is over). Whoever participates in Arena fight, gets full EXP, while others get none.