I downloaded the GNS530 simulator as a .ZIP file and after decompression with winzip have enjoyed it a lot.
It’s fun to play with and actually pretty useful as a flight planning tool. So far as I can determine–sans manual–it doesn’t offer any significant enhancements in terms of NAV or FPL capability over the 430, just a bigger screen. The “default NAV” page is to die for, though.
I’m sort of cheap so I don’t think it would be worth the extra $4K or so over the 430, but I can certainly see how those with play $$ to spend would go for it.