I purchased my 1992 2500/454 burb from Cali and it had just passed their smog requirements and would like to know if there is a benefit in removing all the related equipment? If so how do I go about doing so?

Has anybody removed the stock tbi and installed a aftermarket intake/4 barrel? Would I see an improvement in mpg or decrease? What about performance gains?

first of all why do you want to pull the tbi?

if you want to pull the tbi and smog equipment frist go beat your head aginst a wall severl times then take a break and then do it some more. cause thats what you'll be doing after you pull every thing off.
to pull the tbi I belive you can use the stock intake but you need to remove the water donut witch preheats the fuel mix so you dont get fuel ice'n witch can give you head aches in winter months. next you need a different distributor because the ecm wont know what to do with out the TBI and the sensors on it. I dont know if your truck has a th 400 or 80le if its the 80le you'll need to do something with the TQ lock up or you can run it untill it burns its self up.
OK lets say you've done all the above and your driving it and it feels like it could pull a dead whore out of church well thats cause the grind on the cam dosnt have the spects for a lot of vacum and the huge dish in the pistons isnt helping.

my 2cents is keep the tbi and learn how it works and build on it or spend lots of money on the learning experence