The money that you would lose in a trade-in can be used to get a whole bunch of stuff for your 4runner!
Here is what I would do IF i had a 4runner:
1. Tint front window (not ghetto, but legal) to closely match rear privacy glass (if possible)
2. BFG AT KO 32" (265/70/17) or equivalent AT tire (REVOs, Michelin A/T-2, or Goodyear SilentArmor)...do not go any bigger because of rubbing unless you lift it above 2".
3. Junk running board
4. Rock sliders from ARB or Hanna or Shrockworks...IMHO, the ARB slider/step is the classiest option; however, i hear that ARB is not offering it for the 4runner.

So, check first with ARBUSA.com. See this thread:
http://www.toyota-4runner.org/showthread.php?s=&threadid=30885
These mods should make your 4runner look really cool...waayyy more cooler than any stock FJ! And you would still have a much more practical vehicle than the FJ. There are two additonal steps that you may want to consider to make your 4runner into a monster:
1. 1" front lift to even out the 4runner's stance...the 1" should not cause any issue. This small front lift should get rid of the nosedive/butt lift on the 4runner. In addition, you will get slightly more frontal clearance for off-roading.
2. ARB rear locker with on-board air compressor...this mod will make your 4runner into an off-roading monster! A locker can make you go places where you could not before with confidence. The air compressor will allow you to air up your tires with ease quickly. In addition, i think that it can power air tools too.
If you do all of the mods above, then your 4runner will easily keep up (and beat) > 95% of SUVs/trucks out there.
The above modded 4runner = just as capable as FJ and way more practical.
BTW, i would stay away from adding a front locker...too much stress on the IFS components. With a rear locker + ATRAC-controlled front, you should be plenty capable.