I'd seriously consider dusting off a RISC PC or late model Archimedes instead; ARM26 is a joy to work with compared to 6502 (at least for me) and the RISC OS system is quite beautiful to work with. Plus, I (perhaps naively) figure that there'll be plenty of ARM chips continuing to be shipped in devices where I can somehow get the thing to do what I want, whereas I'm not so sure the 6502 architecture would be so widely useful.
