I agree the intercooler is hardly worth $900. I don't beleive anyone has ever reported any significant improvements in performance, especially not in the quarter mile. You would have a hard time finding a way to waste $900 better than this, for less gain in performance. Denny Raab went 11.0 @ 129 with the stock intercooler, I went 11.7 @ 114, Mike Pearce went 11.7 @ 114, Myclone went 11.9 @ 113; my thought is unless you are faster than these guys you don't need an intercooler upgrade. A friend of mine was running 12.4 @ 106 and put on a huge air to air, top notch best you could buy. He went 0 tenths faster. You read that right. And his MATs were put to shame when compared to a stock intercooler with alcohol injection.
As for the headers I can't say I've heard anybody say "Guys, I just bolted on headers and got back from the track and went X tenths faster!!". I think they improve exhaust flow but Turbo Tony went 10.71 @ 126 in hot humid weather with stock manifolds and many others went low 11s with them. I personally don't plan on doing headers since they seem to be more hassle than they're worth; take up a lot of space, melt & burn shit, they are very prone to cracking, and your under hood heat typically increases greatly, or at least on the trucks I've seen equipped with headers. (Can't vouch for heat coatings' effectiveness or not). If I was you I would reevaluate where my truck's performance stands with what I've got in it and come up with some different ways to spend the money where it will provide maximum return on investment. For $900 you ought to be able to get something that will make you laugh like a little boy when you get on the gas, and I don't think either of the things you mentioned meet that criteria 8)