Mplath1: Another idea, (and I have no idea if this has been done) punish the player for saving outside of a safe town. Not with money as it can become almost too abundant late game in some RPGs. Make your party sacrifice some amount of XP. Maybe half of whatever hasn't been solidified into leveling up. If you were a real sadist you could take XP and have them possibly de-level which would be somewhat realistic. Your highly experienced party somehow got lost in the wilderness with no plan and are blindly wandering? It sounds like your party isn't THAT experienced, so you can save but everyone loses a level. Another option would be to just cut everyone's max HP by 50% until the next time you are able to rest at an inn. Again if you're a sadist you could make it stack or something to discourage spam saves once you took the initial hit.
I *really* don't like this idea.
If you do insist of having a mechanic on these lines, reward the player for not saving for a while rather than punishing the player for saving. Perhaps the player could get stat or XP boosts the longer the player goes without saving for a while. With this said, I still don't like this because it discourages saving, and not saving I see as being a bad habit of many players.
Also, the cut max HP option increases the risk of the player saving themself into a corner in which the player is not strong enough to go from the save to a safe spot (perhaps there's a boss in the way).
Interestingly enough, I have had a similar idea, only it wors with resting rather than saving; as you fight enemies, you'll quickly gain some stat boosts (there is a very reachable cap), but the stat boosts go away when you rest. Resting will be the most convenieng (perhaps only?) way to recover your resource, but if you rest too often, you won't be able to hold on to the stat boost; in particular, resting right before a boss fight might not be a good idea. In game where it's easy to avoid or run away from encounters, this mechanig would encourage the player to fight at least some encounters on their way to the boss (or fight easier encounters if the dungeon is something like Dragon Quest 2's Cave to Rhone, which is a dungeon that has incredibly dangerous encounters later on, but (fortunately) no boss).
Interestingly enough, SaGa Frontier 2 has a mechanic where, the lower your current WP is, the more powerful your martial arts are, and the lower your current SP, the more powerful your spell arts. So, your Firestorm spell might not be strong enough to kill some of the enemies at the start of an event, but will gradually grow in power as the event progresses until it is. (Note that, due to the way SP boosting equipment works, your SP will never start a battle below a certain amount, so you don't need to worry abou running out, and there's still the option of spending LP if you do run out.) With that said, SF2 only lets you rest in town, and in many events (including, rather infamously, the final dungeon), there's no way to do that without ending the event (at which point you can't go back).
JakobFel: My preference is for the ability to save (standard and quicksave) at any point you wish. However, I also understand the issue of save-scumming which can ruin the experience and replayability. Nonetheless, it also can be irritating when you've been working up to a certain result and then, at the eleventh hour, you choose one wrong choice and it ruins the entire thing you were working toward. This is particularly an issue in narrative-driven RPGs, especially ones focused around forming relationships with other characters.
It's also an issue with games that use skill point systems or similar systems that require the player to make irreversible choices wen it comes to character progression. In many of these situations, I like to make one choice, play with it for a bit (without saving), then reload and try a different choice.
JakobFel: EDIT: I should also add that I really do not like when games give you a cost for your saves. That's one of the major flaws that keeps Kingdom Come: Deliverance from being a 10/10 for me.
It's why I never got into Quest for Camelot (early Game Boy Color game).
It's also one of the three reasons I didn't get Breath of Fire 5: Dragon Quarter; the others were the D-Counter, serving as a (turn-based) time limit (which went against what I was looking for in RPGs at the time), and the copy protected save file (which I consider to be a form of DRM).