I bought my Tech 2 three years ago -after the XLR production ended. The memory card was updated to the 2010 GM model year, and works great for my '04. While changes to the Tech 2 for the entire GM lineup have surely occurred since I bought mine, I doubt the XLR has seen major revisions to it's diagnostic software --The Tech 2 works hand in hand with the shop manuals, and those are pretty much "locked down" as well.
The latest revisions to Tech 2 software and procedural changes to the shop manuals are available to dealerships. Again, I doubt there are enough changes to fret over (especially new procedures to open a jammed trunk!)
Dealers are converting from the Tech 2 to a PC-based diagnostic system, but the Tech 2 works great. My old dealership said they'd update my firmware if I wanted to, so it really depends on the relationship you cultivate with yours. I wouldn't let that aspect of Tech 2 ownership dictate whether or not to buy one. Any of the new Tech 2's you buy online should be at the latest rev anyway.
For me, the decision to buy a warranty or a Tech 2 was easy. My car was not eligible for a GMPP and all of the other warranties I researched would not include the Folding Top or associated electronics. Though the salesman said their warranties were bumper-to-bumper, the small print begged to differ.
I find that one of the most problematic issues with the earlier XLRs (04-05) involve the calibration of the top, and my car appears to be no different.
I've fixed a couple of problems using my Tech 2, but it hasn't paid for itself (yet.) I does however give me piece of mind if I have to take it in, since I have a pretty good idea of what's wrong and whether or not it's in my ability to repair the fault or not. I scan the car at least once a quarter, write down what it finds, clear the codes and re-scan after a quick drive. Almost always, the car scans clean. If I see the codes pop up over time, I take note and deal with them according to the shop manual. Dumbs#$t stuff like gas caps that aren't seated and illuminate the MIL light are quickly cleared and forgotten.
Had I spent considerably more on a warranty, I would have a year left and no major repairs to have applied it towards. At least I have a tool I can sell and re-coup at least 50% of the cost later on.
For me, the Tech 2 has been a worthwhile expenditure and allowed me to learn a lot more about these interesting and unique vehicles. Your mileage may vary.