I went through a few phases in building my herd (things like moving from 4 to 5 strings) where I ended up with a bunch of basses I no longer used. There are a couple places in my city that teach kids music (the public schools don't), and I have donated basses to both of those organizations. If you do it one of two at a time, it's pretty easy, over time, to thin a herd substantially - all you have to do is find one bass that is a bit less loved by you than the others, and you're good for a while. I have a few really nice basses, and the schools have 3 or 4 times as many good basses for the kids to learn on. Even though all of those basses are ones I used on gigs, and they were all really good, I've never regretted a single donation.