I've used both the 430/530 and GNS480/CNX80.  As far as operating them goes, they are totally different.  Since you learned to operate a 430, you would have a pretty big learning curve to translate to the GNS480.  I like them both, and actually prefer the 480 because it does more, but then again it's much harder to learn if you plan to use the entire range of features.  If you are thinking about a MX20 (or the new GMX200), then I would recommend the GNS480 since they were designed to operate together.  The GNS480 is more of a Flight Management System than the GNS430.  You can input airways in the GNS480 where you can't on the 430 too.  

Ron Galbraith