I remember ICD products being incompatible with most things as well. I have an old AdSpeed around here somewhere. It was a 68000 clocked at 14 Mhz, a modest speed increase when coupled with some true fast ram, next to worthless without fast ram. I was running an A570 CD drive at the time, never found any accel. compatible with it including AdSpeed.
For what its worth, I've always thought the A500 casing looked great by itself. If you can boost performance/function and still keep that look, it'll be very cool.