Are you planning on having a car in Anchorage or Fairbanks? I think it would be wise for both places. You can take a day in Anchorage and drive along Turnagain Arm to Girdwood and even a bit further. Lots to do/see even in the winter - Potter Marsh is a great place to stop for potential wildlife viewing. Girdwood is a neat town, the Wildlife Conservation Center should be open, driving to the Portage Glacier area is easy and though things are closed, I have seen moose in that area in the past.

I would not rely on the "excursions" for aurora viewing. In fact, if my objective was the aurora I would not stay in the city. I would try and stay somewhere outside the city where you don't even need to drive or get out of your lodging if you don't want. Or at least that makes it easy to peek out the window to see if the aurora is "out" then you can get dressed and go outside to view/photograph it.

The Arctic Circle tours get good revies, though I have only done something like that on my own - a day trip to Barrow using miles and vouchers. But I did it in September, not in the winter! Northern Alaska gets great reviews for their Arctic Circle tours. I am not sure what they offer in the winter, but the fly-drive tours are the best option IMHO.