Wheels do make a huge difference. While it wouldn't make a huge weight difference, some slightly scaled down tires would reduce rolling resistance and give the feeling that the bike was a little easier to pedal. If it were me, and I was really concentrating on getting rid of some weight and make it a bit easier to carry speed and accelerate faster, I would say go with the XT wheelset over the other upgrades for now.

-Moab


(Edit) - P.S. - I don't knwo where you are buying Shimano Deore derrailleurs for $100, unless you mean Deore LX or Deore XT. Even so, I would look around before buying Deore parts for that price. You can get them much cheaper elsewhere.