I have an ibanez rg, and right now it sounds pretty nice through the clean channel on my crate with some reverb. but I'm wondering if I would get better sustain and harmonics if I put in an evolution at the bridge or neck position. am I correct that this is what steve vai uses, and does anyone use them/recommend them?
Yes, they improve sustain and harmonics/

Yes, Steve Vai uses them.

Yes, I have used them and would recommend them, but only for shred - I find that the Evos don't hold up well if you're doing any power chording/riffage.

What kind of Crate are you using?
Ibanez RGA121 | ESP LTD H-1000
Axe-FX Standard
I threw a set into my Jackson. They are pretty cool, but they are really sensitive. If you are a sloppy player they will show it.

You might just want to save the money and put it twords a new amp, depending on what you have.
I have a 2007 Ibanez JEM7VWH, and the stock Dimarzio Evo's are really good, and yes, they are sensitive, but I find with the right amp tone, they sound killer. Through my marshall, or even a POD marshall simulation, I can get a really nice "chug" with power chords, really nice definition, and the clean tones are just gorgeous on any amp I've tried. I find that guitar and the pickups to be the most versatile I've ever tried, works well for any style of music I can play so far, clean, dirty, a little crunch, super high-gain, whatever, just sounds amazing.

I probably don't have as much issues with the sensitivity because I use a noise-gate in general with higher-gain distortion, usually set to the point where there's zero audio when I have my palm resting on the strings.
my bridge Evo is get for metal and pinch harmonics, its a very "tight" sound ^_^
cool, well if I just get one, would it be better to put it in the bridge position or neck position?
someone said their good for shredding... what about clean tones? does it do both pretty well?