I had up to 4 games at one point, and I've found that 1-2 suits my space and desire for now.
I used to think I would get a game and keep it forever if I liked it. Now I'm more content to have 1 or 2 machines and enjoy them thoroughly, rotating them out every once in a while.
I'm also not personally interested in the reusable cab concept (P3, Heighway). That's not to say I won't like their individual games (Alien, etc..), but I don't really care about swapping games in a cab.