I think a built-in merchant refresh would make players bring even more loot. Really you might as well let merchants buy infinite supplies of what they're interested in, and have infinite money. It would save the trip back and forth from the bed.
Even SGS credits shouldn't exist, since it'd be just a trip from the bed to Jonas/Blaine.
The two time-sensitive events I can think of (merchants and super steel) are there exactly so people don't have to do scummy gameplay. They're meant to make you move on and take what they get.
The only thing I agree is that certain components can be essential to certain builds and legitimately not appear anywhere until you're way past level 15. Even some parts like a low quality electroshock generator for your taser might just never appear before Ezra moves on to higher quality goods. I think this should be mean more fixed goods on vendors and more guaranteed loot in critical spots, not vendor refresh