Buying is easy, selling is hard. I have sold off more than half of my games and it has been a liberating experience. I have a big stack of disposable cash, room in my house, less to maintain, and a few empty slots in case a deal comes up. The hardest part of selling games is not immediately filling the spot.
You have an amazing collection, but it might be time to share it by letting some of them go. New collectors complain about never finding deals or classic games, so you could provide both. If you really care about making money on pinball, you might be in for the wrong reasons.