That last part is important, by the way, because the courtyard missions are fucking huge. Of course, these upgrades become less viable if you're playing with a time limited difficulty level, but that arguably makes it a more interesting decision as to whether or not to go for them. The increased critical hit chance for bounty hunters/grave robbers/highwaymen, the increased status chances for plague doctors, and the innate stress resistance for jesters are all wonderful upgrades the extra action points during camping for abominations/hellions/lepers is ridiculous, especially since it can't be substituted with an accessory like most of the other class perks can and the extra benefits for having high torchlight make playing in brightness (something that you should be doing already, in most cases) even more rewarding. I wasn't too keen on this at first because I'd thought that the number of heirlooms required for them was excessive enough that you wouldn't get much actual benefit from them by the time you can afford them, but that ended up not being the case. Third, killing bosses can reward you with blueprints, which are used to unlock special upgrades that cost a fuckton of heirlooms. Stress is an issue when it happens in dungeons, but in town, it's just a matter of not using that character for a little while to recover it (or, if it was a shitty character anyway, just dismiss them). At worst, you'll waste some money and gain a bit of extra stress on your characters. What makes it too forgiving in the case of Darkest Dungeon is being able to retreat from individual fights with very high chances of success and being able to retreat from whole missions with very little consequences. This is, of course, standard procedure for playing a roguelike, so that's hardly anything novel, nor is it something that negates challenge innately.

The way to assure your success is to first and foremost reduce your reliance on the RNG as much as possible, then to stack the odds in your favor as much as possible, and only then to take advantage of characters having that final safeguard against dying.

The death's door mechanic is part of this, but it's really just a last resort. This all underscores another point: Darkest Dungeon is too forgiving to really be considered a hard game.

Darkest dungeon abomination virtue