I'd welcome a 430 RT with open arms! I am in a pickle right now with off cam lighting - currently i have 1 600 Rt and a pair of 430's (and cheap cactus triggers). I'd love to add 1-2 flashes and am in the deciding stage as to how to proceed. Spend a whole crap ton of $$$ on going all RT, or, spend a whole lot less and go with cheaper flashes and cheaper triggers..
Pros to going all 600 -
one system that is good
ability to control the power of all flashes from the camera
worth repeating, expensive!!!
And again - expensive - I am not just thinking initial cost - as these would be mostly used off camera, on lightstands, in location environs (what happens when you have a stand in the water, set low, tide is coming in as your shooting and the flash gets dunked ---flash on stand but it's windy...TIMBER!!!!!!) I have watched my lightstands fall on enough locations that the idea of $600 flashes scares me.
With all that said, the 430 option would still be close to $400....uggg...thinking cheaper manual flashes will be my future for a while...but the 600 system is really tempting