Advantages of XP30: more sounds (if you like the 3 on-board expansions), a bit easier to transport from place to place.

Advantages of XP60: if the boards that come installed on the XP30 don't suit you more than the other available expansion cards, the 60 lets you add 4 boards of your choice instead of just 2; floppy disk drive (floppies are so incredibly cheap!); much better user interface/display...going from menu to menu and programming sounds is much, much easier on the 60; even if you use your software sequencer, the 60's onboard sequencer is nice to have as a little musical idea "notepad" and it is great to have if you want to take the 60 on the road and do some composition.