I took a fantastic trip to Alaska last fall. I suggest you spent as little time in Anchorage as possible. If you feel the need, do some sight seeing in the city on your last day before you leave. The lake where the float planes take off and land is neat. Their is so much else to see in Alaska.

In Seward I would suggest spending 2 nights. You can hike up a short trail to Exit Glacier. I took the all day Saltwater Lodge whale/wildlife/glacier cruise. They do cruises and also have lodging. I myself chose to stay at a motel near the marina. Their cruise is on a smaller boat and is limited to 15 people. We had only 4 people on our cruise. It was wonderful. Highly recommended. As a precaution take some dramimine 1 hour before the cruise. Alaskasaltwaterlodge.com

Denali National Park is fantastic. It deserves as much time as you can allow. I spent 1 night at the entrance and 3 nights inside the park at the Skyline Lodge. It's the lodge where the Kantishana Air Taxi pilots stay. They only have a few rooms (no bathrooms in the room). It's price is much lower than all of the other in the park lodges. You can ride the bus in or have Kat Air pick you up at the entrance. They also do all the scenic flights in the park. Also well worth the price. You ride the park bus to get around.
Their website is www.katair.com.