Best upgrade for any bike, especially a commuter would be to convert your wheel set to Stan's No Tubes. www.notubes.com
You save weight because you're getting rid of the tubes, (probably more savings than upgrading to an XT wheel set)
You don't have to worry about getting a flat unless you run pressure low enough to register zero on a gauge.
You can either buy a kit and convert it yourself, or ask the LBS if they'll do it for you.
This is a relatively inexpensive upgrade as well. And well worth the $80-$100