Welcome aboard!
1) Sounds like power steering fluid but there's no way to tell from your description whether it would be something as cheap as replacing a leaky hose or as expensive as replacing the pump or power steering unit itself. Sorry - no way to answer this really.
2) Yes, the shocks are still available. The bad news is that one of the reasons they're still available is because they are outrageously expensive! Last time I checked they were $427 each but that was probably two years ago. They may have gone up since then. The good news is they can be rebuilt for a lot less than that.
3) Mileage sounds about right. On average, I get 17mpg. And that's fairly accurate. I've checked my speedo/odo with a GPS and it's only about 2% off at 70mph. The best I've gotten was a little over 21mpg but I had and egg taped to the bottom of my shoe for 2/3 of that tank. I probably could have eeked out another mpg or two but I just couldn't stand to drive that way any longer. The worst mileage was when I first got the VX. You have to realize I was coming from a ponderous 3/4 ton diesel pickup truck so the VX felt like a frisky little go-kart and that's the way I drove it - which earned me 11 mpg and two speeding tickets within the first month.
You really should drive a Vehicross before you buy one. They're not for everybody. The rough ride is probably the #1 complaint. Being a mountain biker, you're more used to the pounding than most though so you would probably be alright. Then you just have to deal with the #2 complaint which is lack of cup holders... :bgwg: