Wasting 5 minutes going back and forth to save 150 copper is basically running a deficit, because in that 5 minutes you could easily earn 150 copper exploring, looting, killing. It's like taking an unpaid leave from your workplace to go to the store and get that 50% sale on a loaf of bread. There is no incentive to waste time this way.
That is, of course, more true later in the game. But you're forgetting that (at least as far in the game as I've played) there is no renewable source of income, so it's not a completely fair comparison. It would suck to miss buying that great late-game item for your character by 86 copper because you camped one too many times. You're also forgetting the other incentives the game provides for running to town.
Yeah. That's not going to happen, not unless you're buying 300 camping supplies. By the way, the stronghold is a renewable source of income to infinity in the form of taxes. Given that you get several hundred copper, It simply isn't a valid calculation.
Of course there are other incentives for visiting town/stronghold. You're meant to have gameplay - it would suck if there were no reasons to visit the stronghold. The point is that there isn't a strong incentive to keep running back to town in the middle of a dungeon just to sleep at an inn and save your 75 copper.
I've just gone through 4 levels of Od Nua without running back to town. That's not because I'm awesome (people will play on different difficulties with different sized and composed parties). I just find that when I try to go as many battles as possible without resting it adds to the tension, it adds to the tactical diversity (if Eder is on 2 health I can't frontline him like I always do), and it adds to the fun.
I'm sure somebody will make a rest-anywhere mod, of course, so that if you want to rest after every battle, or whatever other combination, you can.
I am currently annoyed that money is finite.
How you get infinite money with the stronghold? I thought that you could only get taxes after a number of quests (and obviously those are limited, or there are repeatable quests? Or randomly generated quests?)