Well clearly i dont know what i'm talking about so i guess i should just go. but the truth is, it's arguable that any of these bolt-on mods for 4.0's add any real horsepower. if you aren't adding forced induction, or changing heads, cam, or stroke, there isn't a whole lot you can do to change the performance of an engine, all the stock parts are adequate for the stock internals of the engine. so gains are little to none.
today i did a 0-60 in my bone stock (daily driver) 93 explorer 4x4. it was 15 seconds. but i had an axle in the back weighting it down a little.. even though, that's not very fast. i think if you did all these bolt on mods (air filter, air box, intake system, MAF, TB, headers, exhaust, under-drive pulleys, etc) and you got it down to 14 seconds, you'd be doing pretty good. i dont think it's worth the money, and hassle for that though.
by the way, is that a 4.0 in you're avitar? it looks like it has some of those proven-worthless headers on it.