The KS version should not be a problem, one can always get a new kickstart from softhut etc... I'm more interested in one of the C64s (the A500 is just too similar to my A1200, the miser in me wouldn't stop complaining...), but if I were to buy an A500 I'd most probably fit it with a kickstart switcher, to have the least compatibility problems.
Watch out though, opening your A500 will void your warranty... :-P