I just got my camper (8' Ranger II) on a 06 Tacoma Access Cab 4x4 back in September...drove it back from Boulder CO to Southern California with no suspension mod whatsoever...that was a bit stressfull, but all in all it worked and I even got some very slow speed offroading in on the trip back...since then I put the airbags and daystar cradles and what a difference! Even with the crappy stock shocks it's night and day. The shocks will likely wear out quick now, but the airbags do make a huge difference and I like the ability to be adjustable. Since I had brand new TSB leaves, I felt like keeping them. I may do an icon add a leaf later on if i decide i want the lift. It removes the overload spring, but that is what the airbag would be for at that point.
I wrestled back and forth with this for quite a while myself. I read a lot on the boards (read the entire 30 plus page thread on tacomaworld for example). In the end the firestone airbag system is the only thing you can buy that you can use to change your ride after you install it (well the $1000+ Fox shocks have damping adjusters too). With all of the other spring options, you won't know if it's good or bad until after you install it ($$), get the truck realigned ($) and take it for a spin. For that reason, I think airbags are a good place to start. Even if it doesn't end up being the right fit or the only thing you need to do, at least you'll have adjustable bumpstops.
Beyond that, find someone with your exact setup and desires who's already made all of the mistakes and decide to trust them without question. Better yet, buy the camper truck combo mentioned above and just go camping!