Well, I get more than two days out of the heads...

I don't think I've heard of them burning out that quickly, in general. Just how high are you dialing up your voltage?
I noticed that with ViVi heads you can really go to town with high voltage, uuthey don't tend to give dry hits, expecially when the tank is full, but you can surely burn them out if the voltage is too high for the resistance...
I haven't had it that long, or used it that much, so I can't give you an average lifespan.
As far as Fluxos and Stardusts are concerned:
Fluxos live a looooooong time. I've had some last over three months. No kidding. But some folks find them fiddly. Some don't.
Stardusts' life span has been, in my experience, more limited by the tubes cracking than anything else. I've never had one live less than a month, but keep in mind that I don't use high voltage either. I use reg. resistance at around 3.7 to 4 V on the average, and less than that on some juices.
But, basically, the lifespan on both is really good.