I dont think that buying a bigger space makes sense. Im not sure if your house situation, but is knocking a wall down for a bigger space an option?
Try local barcades.
Travel to more pinball shows.
Do trades with local collectors.
Buy project machines to fix up and trade or sell later.
Join local pinball clubs. It allows you to play more, meet more pinhead friends, and get better at playing.
I would also consider trimming down to your ultimate limited collection (whatever your space holds), and selling off the rest.
You coukd also just hold on to what you have, and only trade when there us something you 'have to have.' If you trade smartly, you wont lose any money or gameroom value.