Couple simple things that would help:
Going into a seperate interface to sell is WAAAAY to clumsy. I would suggest allowing you to long press on a mod anywhere(equiped, in mailbox, etc) and sell it(with confirm box). The destroy button should just be replaced with sell. That's just silly.
Long term I think some sort of mod consme is answer:
Basicly, you feed a mod to another mod and this allows you to customize your mods. Like:
Basicly, each secondary has a max possibel value and feeding mods with matching secondaries adds some perentage.
If say, Defence has a max value of 30(I just picked something), then consuming a mod with a Defence value of 10 to one with a defence value of 20 makes it 20.5 or something(fractions don't count, but are tracked)).
unmatching ones go into some pool that can be used to level a secondary(lower conversion rate of course)
This way, you would slowly build your mods toward so eventual max and "finish" a mod. This would even out the rng a bit also.
This way you could slowly build mods you want.