good question.
i haven't 1cc'd any shmups i own, well except borderliner ranger x, and after completing that game I haven't touched it since.. I'd only touch it again if I wanted to try for a higher score or maybe just 1 life it. I certainly wouldn't want to get rid of it though because I like it so much.
It's also strange that although I can play all the games mame emulates, I hardly put as much time into them as I do with the games I own. I just feel more motivated to try hard at playing a shmup I own compared to one on mame. Maybe its because they are a physical item you own, so it just has a greater value to get the most out of it.
It's also pretty hard for me to switch between playing multiple shooters, I can only focus on 1 or 2 that I really play seriously, otherwise I don't feel like I'm making progress. I dont think that would stop me from owning a bunch of games though, there would just be a lot that would need to wait in line to be played.
and then there are pc games, those come before shmups, i buy 'em for 50 bux when they come out and then play through them in less than a week (or continue to play multiplayer for a year), they are rewarding to play through and experience but it's not the same type of thing as a major hiscore or 1cc.
It's also hard for me to think of buying pc games as a collecting type of thing, it's stuff that could get thrown out after I've beat it and I wouldn't mind.