The S520 doesn't have a middle single coil.. which makes it slightly less versatile than the S470... And this year, its way overpriced...
I'd say go for the S470... its more bang for buck.
Anyway, the S series has a punchy tone.... but fat? No... don't expect les paul fatness... its got good thickness for a thin guitar and thats it.
Btw, I have a 2002 S520EX...