Hi EWatt!
I can't comment on upgrading from your older verson of 4.X, but I am still on 5.0 and don't see why there would be any issues at all in upgrading. Apple is pretty good about integration with older versions without too many problems. You should just take a deep breath and go for it! I am very much looking forward to 6.0...seems to have a lot of nice new features.
I have visited the Apple store in Pineville (South Park Mall) and it was professional and helpful as most stores are. I was recently in Northlake Mall where the other Charlotte Apple store is, but did nothing other than take a peek inside. Didn't really need anything and didn't want to drool over all the stuff I can't have right now.... LOL!
Do you live in NC or SC?