Preface to this question: I have ideas like other people breathe.
The last time I bothered to sit down and count my characters - which was about 5 years ago - I had over 400 characters scattered across 35+ fictional universes and stories, and that number has only grown since. This is counting ancient stories I never finished, stories I intended to finish but then scrapped completely, stories in various stages of development, stories I've already finished, and stuff I'm working on at the moment.
I'm kind of a hoarder when it comes to stuff like this. Nothing ever really gets thrown away. I keep everything lying around (neatly organised by project-folders, of course, so I can find it again).
This doesn't mean I cling to old ideas and find it hard to sacrifice characters for the good of the story - it just means that once they've been cut out, I stick them in a little box of spare parts labelled "Ideas and characters", which I can then revisit whenever I need to.
To pick one random example; when I was seventeen, I wrote a story about a world made up of islands floating in the air, and some of the characters I had were pirates aboard a flying ship. The story went nowhere in the end, and I scrapped the entire fictional universe, along with it, but I kept the ideas around in my box of spare parts. And then, when I was about 21-22, I invented another story, in another fictional universe which had air-travel by flying ships, and found myself in need of some characters. So I reached into the box, pulled out the cast of that old story, dusted them off, tweaked a few things, turned them from pirates into a scrappy air-navy, and voilá, they had a new home and a new story.
I do stuff like that all the time. Everything serves a purpose, even when the original purpose they were invented for no longer exists for them. I'm the storytelling-equivalent to an old lady who always keeps a piece of old string in her purse, just in case.
I let go of the old stuff that wasn't working, but I keep the stuff that might. Even if it doesn't end up in the story I originally intended, and even if I tweak and change a bunch of stuff the next time I use them, and even if the old story gets entirely scrapped, I keep the spare parts. I can cobble together pretty much anything from spare parts!