For a solution inside the A500... better wait for Zeus68k accelerator which looks QUITE promising and exciting!
Also you can go the kipper2k 4-8MB Fast RAM + IDE68k approach and stick with 68000 or an beefed a little 68010 for some WHDLoad fun.
ACA500 is indeed an low spec and cost sidecar adapter. Will have 2MB (or 4MB upon request) of Fast RAM, 2xCF adapters and 68000@14MHz. It has an A1200 accelerator connector, where you can connect for sure the line of ACA1231/1232 accelerators (ACA1230 not supported as long as other accelerators by Blizzard and Apollo).
As for looks... anyone has it's own opinion.
For me... despite it's features (with an accelerator connected) the look is rather crappy.
Unless you manage to mod it inside a nice sidecar case as GVP 530... sticking 2xAdapters in the side of your A500... will be Frankensteinish approach.
The first prototype which was Vertical instead of the new Horizontal version was really a bad joke.
