If it were me, I would spend an extra night in Seward if of interest. Lots of things to do/see there - Exit Glacier, Sealife Center, hiking. Otherwise on your way back from Seward to Anchorage consider the Prince William Sound tour from Whittier.

>>6 - Denali NP: Nothing planned. Suggestions?

I would suggest a second day on the shuttle bus. Book both days to Wonder Lake, but decide the day of the trip if you will go all the way there or just get off at Eielson. Some great places within the park to hike.

>>7 - Drive back to ANC for red eye flight

You can see/do alot in Anchorage this day if you leave Denali NP in the morning. Depart about 8am, back in Anchorage 1-2pm. Then you can do some of the things gardyloo mentioned above. Though I somewhat agree with him, there is some truth that Alaska is just 1/2 hour from Anchorage