There wasn't ever an issue on this thread whether an A1200 is better than an A600! It's silly to just compare these 2.
The OP mentioned wanting an A1200 in his first post. I'm just sayin' that if he can only justify the one, he's probably better off holding out for the A1200.
As for the A500 over the A600, I'd pick the A600 any day. Smaller footprint, more modern hardware. ECS/2MB Chip/IDE/PCMCIA and with all the accessories that Jens makes for it, it's a far more interesting machine.
But if you've got an A1200 for expanding like mad and a pre-existing A500 for the old-skool experience, do you really need an A600 as well?
Again, it all depends on where you're going. It's a hobby. My A3000 is pretty pointless since I have an A1200 and an A4000, but it's still cool to have the 3k. I'm toying with the idea of getting another A600, I gave my last one away.