You can also glean information from FlyerTalk on how best to use your US Air miles. I can't help you since my miles are with Continental, but there's no reason why you shouldn't be able to book the flights to destinations you want, it's just a matter of how many miles you're willing to spend and how you want to get there. I notice that US Air has four tiers on their mileage chart, while CO just has two: EasyPass and SaverPass. For CZM, I'm guess you were looking at the Caribbean chart which lists an "Off Peak" coach fare of 25,000 miles. However, I bet US Air considers CZM to be in Mexico and there is no Off Peak rate for Mexico. The 80,000 they quoted you was the High rate. The trick is to get something better than the High rate so you could at least knock the fare down to 60,000 (Medium) or 35,000 (Low).
On CO, if I'm willing to pay the Easy rate (60,000 miles, corresponding to US Air's Medium), I can fly when and how I want. On the other hand, finding flights using the Saver rate (35,000 miles, corresponding to US Air's Low) can be more difficult if not impossible. For instance, getting a Saver rate on first class tix with several months notice (60,000 on CO), caused me to book three legs from ONT to CZM, the first two on US Air. The only way I could find any seats on the more direct flights (1 stop in IAH) would be to use the Easy rate and I make a personal point to never use the Easy rate unless, I suppose, it were a matter of life and death. By maneuvering my schedule to accommodate the Saver rate, I'm basically flying first-class for what it would normally cost me to fly in coach on the Easy Rate. On the other hand, if adding a second stop en-route causes me to miss a connection, I'm screwed, so it's not only a PITA to "save" miles but it adds risk as well.
Check FlyerTalk's US Air board for tips on how to get the lower tier rates, though it will take a lot of reading and searching if you're new to the game - it really is a game of chance since airline fares, both paid and mileage, are so unpredictable. IMO, the best use of several hundred thousand miles would be to book first/business-class seats to Asia for a mind-blowing dive (and cultural) trip. Since the flights are so long and so expensive, you really get your "miles worth" versus short domestic flights.