Want to get right back into it and happy to lay good dollars down for a 600 (or even a 1200, though i hear they're incompatible with a lot of older games? - true / false?) ...
It is true. A1200 is incompatible with lot of old games. But you can use WHDLoad (if you have HD and more RAM) which helps A1200 to load more games. Amiga 600 is not more compatible than A1200 and I would choose A1200 if there is no A500 option.