So it's worth it to cannibalize several things to get a fully repaired item rather then selling 10 crappy items?
Not quite, the better something's condition is the better it's price, but only to a degree. It really requires some experimentation to find the optimal point to sell or repair. I know I had enough shit lying around (on account of I'd clear out several areas and just throw it in a locker in my house to deal with later when I could better repair/sell it) that I did some tests and came up with some optimal rules of thumb, or course I don't remember any of them.
Really the quality of items isn't a terrible issue in generating money, the biggest problem is finding a merchant with enough caps. The only merchants who have worthwhile amounts are the travelling ones after the associated quest, and they can die in an unmodded game (thank you console commands), not to mention the fact that they're schedules tend to get wonky mid to late game (probably due to encounters with enemies and/or getting stuck on terrain features. Honestly, I'm tempted to just add a merchant who has lots of caps and 100 Repair Skill via mod to some convenient location, as trying to sell stuff in the vanilla game (late game) is more tedius than anything else. Generally speaking, if I find an aspect of a game tedius thats not a good sign for the devs. The fact that the same lategame economy issues tended to creep into all Bethesda games, make me think it's an issue that they've never bothered with, indicating they don't get too many complaints about it (or simply don't care). I suppose my OCD induced compulsions to collect everything from slain enemies, and to get the best possible value for my stuff doesn't help either.
I should note that for those on the PC who don't want to use mods, there is a console command that lets you repair items for a price using your own repair skill. Where the money disapears to is a rather amusing though, as apparently paying myself to do a job, does infact incurr labor fees that I refuse to share with myself (must be some sort of pension plan
).