Did it on my old fox body. contoured it / funneled it into and away from the blade. Also milled the shaft down. All in all not a huge difference. But it was free and didn't hurt anything.
the stock tb is smooth enough, polishing the inside won't do anything. if you don't believe me check for yourself. take off the air intake open the throttle and run your finger over it
the plenum on the other hand might be worth cleaning up a bit. it might give you 2 more hp at redline but why not, it's free and it's something to do on a weekend afternoon
This is not difficult to do. I once did a write up on this, but it was lost in the crash.
Best thing to do is break the throttle body down and remove the throttle plate. This makes it easier to do. Just be sure you put it back in right and get the screws tight so they don't fall out on you.
All you really need to do this is a couple different grits of sandpaper down to a 200 grit. For a nice smooth finish, a 320 grit sanding block from the home finishing section of Wal-mart will work. Finally, some metal polish. All in all, it will look great. As for porting the upper intake, thats a bit more difficult and far more time consuming than just doing the throttle body.