There is typically a fare sale for the summer months at some point in the spring. As a warning, consider yourself very lucky if you can find a saver award seat to anywhere in Alaska in the summer. I would use the $50 voucher.

As a frequent IAH traveler, I can tell you that aside from being a long flight, it's surprisingly easy to get from Houston to Alaska. Most Alaskan cities are one stop away from Houston (or nonstop in Anchorage's case); with CO's regular nonstops from IAH to Seattle and Anchorage, it's not that tricky to get to where you want to go.

Have fun!