It depends what defines "fun" for you (and what your space limitations are).
If fun revolves around hanging out with friends, socializing and playing quick multiplayer $1.00 games, then a collection of EM and SS games would be the way to go, and $20K would easily scratch the itch and leave plenty of money for pizza and drinks. Playing these games solo can be fun, but they are designed to be quick where a player does not camp out on the game.
If fun is playing a game for a long period of time devising new scoring strategies and watching video screens, then perhaps some premium modern games (which often have more features/modified rules) would be the way to go. These of course add up fast and 20k should get 2 games, maybe 3 depending on what you choose.
If you like both worlds, then get one modern premium pin with a known deep and broad ruleset (which will take about 1/3 to 1/2 your 20K budget), some SS and multiplayer EM games and there you go. (Note: Wedgeheads are generally not fun to play with friends).
Bottom line: However you define fun, a quantity of decent games, and even of different eras, is going to be better than 1 or 2 singular high-priced games.
