How many comics is “enough”?
This is the difference between a collector and a completist.
The collector will get only what is needed, and cull the rest. The completist will get everything because they feel they have to. And comics is rife with both. It's actually geared toward both. How many other mediums can you say you have a complete run of something, going through several volumes, all the way back to the first issuance of the thing? Not many.
The thing with being a completist, though, is that you start to run out of space. It may take some time, but eventually, your collection can become unwieldy. If you're a collector, then you can start to think about culling your collection. If you're a completist, then you're thinking of ways of making more space.
I'm not a completist. I've broken runs of things on purpose. I broke a run of X-Men in a vote with my wallet because Chuck Austen was single-handedly destroying the franchise. I broke a run of Teen Titans because Rob Liefeld came onboard for a couple of issues, and I refuse to put money in that creator's pocket.
However, I've been collecting comics for a very long time. I've got just about 40 long boxes of comics, and as I go through them, I'm finding that a lot of what I have didn't make that big of an impression on me. So I'm downsizing. 40 long boxes is a lot of comics. I'm trying to get that down to 20. There are certain things that I'm keeping, like everything before 1980, all the various incarnations of Spider-Man, all the Avengers, all the Hulk and all the Daredevil. What I'm getting rid of is the overwhelming bulk of the DC books I have, as well as most of the Image stuff. It's pretty strange. I'm finding that it isn't as difficult as I thought it would be.
So I'm a collector, not a completist. And I feel pretty good about it.
Which one are you?