Post-purchase dissonance is normal. We all suffer from it from time to time, usually just after we've spent a chunk of change whilst knowing that there is a slightly better (perhaps marginally superior) model a bit further up the product line.
Two things I will say though: (i) usually it is better to get the latest model, and pony-up the extra cash (after a few months or even years it will seem worth it), and (ii) the additional features in the newer model are typically there as a result of photographer demand e.g. the colour gel filters (and holder) that come with the 600EX-RT and of course the built-in radio trigger - line of sight is a real pain when you're using multiple strobes (I've triggered 3 flash units with the IR trigger in my 7D) especially with the annoying blinking red AF-lights on the slave units that I have to angle towards the direction of my DSLR.
Notwithstanding all of the above, Canon gear retains a decent used market price, so have fun with your strobes (stick your 60D on a tripod in the garden @ night and use 2nd-curtain on your 580-II and try painting with light, or stick a macro lens on and shoot Orchids close-up with 2 or more strobes in the dark, the results are fun), and when you've mastered flash photography, you can always trade-up.
