I manage mine by not buying a larger safe. My self imposed rule is that all my guns have to fit in my safe. So while my collection has not increased in size, it's quality has gotten markedly better over the years.
I have to admit that I have recently broken my rule and have taken advantage of some available space in my son's safe. All we can do is try......
I decided to follow the same path as Bob. Just beginning the path to upgrade the quality while keeping the numbers similar. Although there are a few that will stay regardless, just for sentimental reasons.
I only started about 6 years ago to actually collect and recently got to the maximum capacity of the safe (it has changed over time because I have customized the interior to increase capacity LOL). I recently sold a couple of guns that don't fit the direction my tastes have gone in and gave away a .22lr to some kids who needed one.
Now when I am thinking about what I may buy next, I am also thinking about what will leave the nest. It's heartbreaking! LOL