[mindless]

Been skiing and boarding since I was 5. I'm 26 now, and I've also taught a few different people to ski and/or board.
1) If you're going to ski, definitely get your skis tuned. There can occasionally be a safety issue, but if the snow conditions are poor, which even in Colorado in December is a possibility, you will be very thankful that you have tuned skis with sharp edges. Given your level, you can get away with having it done once/year.

2) Given that you're out there for a week and your current level, you probably should pick up snowboarding. Depending on your aptitude, you'll spend the first two days or so falling constantly and somewhat bruised. However, by the third day you should be able to get down the trails that you're currently skiing. By the end of the week you should be able to get down just about any non-mogul/double black run. It's much easier to learn to snowboard if you have a week.

3) (an addendum) If you ski, I'd suggest taking a couple lessons. While shaped skis have made things a lot easier, a few lessons will often make a big difference, especially at someone's level that you've described.