Hmm, ok, for some reason when you mentioned that you use ZBrush I assumed you were a regular user. One question: in Photoshop, do you draw anything or just work with textures? Cause I think I misinterpreted your work habits, if you don't draw or sculpt often, maybe you could settle for a Bamboo just fine. But if you intend on getting some serious drawing/sculpting going on then by all means get an Intuos.
The differences are huge between the models. Bamboo is an entry level tablet for casual users, it's aimed at people looking for a fun gadget to play with, to write handwritten notes and letters on their computers and occasionally make a drawing or two, while the Intuos is aimed directly at artists and is built with this in mind. The Bamboo doesn't even have different sizes as far as I'm concerned. Intuos comes in different sizes, has several different accessories such as pens and pen tips, has much better pressure sensitivity, better planned shortcut keys (and touch strips, which I think the Bamboo lacks).
Either way, it all comes to how heavily you see yourself using it. If you mostly just model with a mouse and make photosourced textures in PS (as in not handpainted) and don't draw/paint/sculpt I think you could do well with a Bamboo, but if you plan on doing these in the future just get the Intuos instead. If you have the money to burn on one I'm sure you're not going to regret it.