Sorry but I don't personally see a big market for CD32 accelerators, yes SX32's go for a lot on eBay but that's just the usual supply and demand thing.
People generally like to upgrade their 600's to make them a better WB machine and to play the more demanding WHDLOAD's (to skip the pain of using floppy discs).
A CD32 as standard can already play lots of original game rips easily straight from CDROM. I think even the market for a new 500 accelerator would be quite small.
On my personal 'most wanted' list is of course the IndivisionAGA Mrk2 and an updated SATA/FPGA based Ide-Fix express
Looking much further to the future, a 100 MIPS FPGA based accelerator (using the 020 softcore already in development) with a nice fat wedge of RAM would be very handy