The camshaft specs between all of the uz motors are nearly identical as far as lift and duration. The valvetrain will only breathe to a certain rpm given several things such as valve diameter, lift, and duration. After that its the flow of the head. Since the 2uz is larger displacement with the same cams as the vvti 1uz and the 3uz its pretty much hampered by the fact that it can't breathe. To a point a better flowing set of heads should help, but to make more power you will need it to rev, and thats going to mean a set of cams. I would assume that the 1uz vvti high lift cams would fit in the 2uz heads but thats just a hunch. The shorter runner intake from a 3u will lessen torque, but let it breathe up top. Getting a dyno chart of the vehicle for a base run and seeing where the curves are strongest, then finding out weather the power curve holds to where the cams lose their breathing capacity (given the stock valvetrain components) will tell you if the 3uz intake will really make you much more hp. My assumption is that the bulk of the power will be gained by cams and a remap of the computer (if possible) Use of a good set of headers will be necessary as I'm sure the stock ones flow like crap just like every other uz exhaust manifold does. compared to even a half decent set of headers that is.
If easy power is what you're looking for, then there's always superchargers. Either way, cams really are the main restriction in the stock running gear.