My brother and I had 10 systems hooked up on 3 tvs at one point. The games we kept either in cabinets, on dvd shelves, or in bins. We realized that was insane, so we began to store systems in the garage, and swap them periodically. Not only does that save space, but it makes you enjoy games more often. Over the last couple years we sold 5 of those systems, and then had 5 hooked up on 2 tvs. Recently, my brother took 2 more systems to college, and at this point I have a PS2 hooked up in the living room, and an NES and Genesis in a box in the attic. If I feel like pulling them out it only takes about 10 minutes to hook them up.
I know that was a long rant, but the point I'm trying to make is that it's possible to own a whole lot of systems and not worry to much about space. I know not everyone has 3 tvs, but a closet and one tv will do just fine. I've sold a few systems, but it was fun having them for a while, so if you have the cash you should go ebay shopping and experiment with new systems; you'll figure out storage issues after you but them.
I have five systems but a
he has 23 systems and some of the older ones are huge not to mention 1000's of games are listed and counting. He's going to have to add a PS3 and a Wii soon enough so make that 25 systems and hundreds more reviews to come in the future. Add in a bunch of handhelds, their games and the 23 systems peripherals(controllers, steering wheels, memory cards) and that is a monstrous collection that requires some serious room..