Just wait until you have to deal with the recycle time.
Yes, I can imagine advantages of the new flash's short recycle times and better cooling, like eg professional photographers at graduations where they
have to shoot people in really quick succession with a camera mounted flash.
However, I very rarely come into such situations, and when I do, an external battery pack almost always does the trick for me. And when the 600 flash heats up too much, I have to exchange it for a spare one, which is a (small but manageable) pain, true.
I am much more often in a situation where I have to work slower but with more (like: 4) light sources, eg doing portraits of employees for a company. In those situations I very rarely encounter a flash not recharging quickly enough, because I always use freshly recharged NiMh batteries and rarely fire at full power, which reduces recharging times a lot. And if I do encounter recharging issues it is when I take a 2nd photo when the subject blinked his eyes, and then also the new EL-1 or studio-strobes would recharge too slowly.
So yes, of course the EL1 would be better. Worth that much money? The 600 already stretched my budget...
A small detail that I really like in the 600 mark 1: it has exchangeable colour gels, which are very handy if I want to work with colours other than CTO (not that I did this too often, but still). They dropped that on the mark 2 and also on the EL-1 in exchange for fixed coulour filters, a design decison I find strange.