Well, there are two main things to compare: the guide number, and the radio vs optical TTL.
Guide number is obvious - the 600 RT can put out a lot more light than the 430. What difference that makes practically depends on its use.
The remote technology differences also depend on your usage. There are two main weaknesses of the optical TTL system that I can think of. Backlighting or rim lighting is very difficult to get consistently, since the subject obscures the line of sight to the flash, and using the flash outdoors with bright sunshine makes it hard for the slave to detect the pre-flash signal.
If neither of these cases affect you, and you never have to light up medium sized rooms, then there's no practical difference, but if you might shoot in any of these situations, then the difference will be huge.
The benefit of the RT system over cheaper E-TTL radio remotes is that everything is compact and self-contained. No extra dongles to worry about. But apart from that, and the "new hotness" factor, you can achieve the same results for cheaper using Phottix Odins or PocketWizard TT1/TT5's.