For me it is more important that there is a variety of gear. I would love for there to be a handful of SMG's where it isn't as straight forward as gun a is not as good as gun b. Maybe I want to choose a particular brand, favor a bigger clip, available firing modes, mod slots, etc. There are so many different parameters you can play with that you could easily have a dozen side grade options for each gear type at every power tier.
After that, I'm not opposed to rarity levels though I'd prefer if it didn't correspond to different weapons (all uzi-9's are green and all suranam's are white), but rather variants like shoddy, stock, custom, milspec, etc so for example:
uzi-9
-grey - "2nd hand" probably busted but then jury-rigged into "working"
-white - new, factory spec
-green - custom build with some premium components
...
-orange - next gen working prototype, every piece is extremely high grade/low-tolerance, this is the best form this gun can exist (before mods).
Then let me mod all of that, though I'm fine with different pieces of gear having different degrees of modibility, like a line that has NO customization, another that is made to be completely modular, and then a few lines in between.
For the tiers I don't think general stats/skills should gate use, but I see options not being available under a certain street cred rating, and better things should cost more.