Here's another vote for Fairbanks. I was just up there last week, and we had visible aurora on both clear nights during the week we were there. I don't know that you can really "pad days" because it's totally dependent on cloud cover.

While I was there, it was very obvious that everything was in the process of shutting down for the season. The resort our Denali tour left from was shutting down for the season the next day. Same thing with the Riverboat Discovery in Fairbanks. I'm sure there's still stuff to do (definitely more than in Barrow), just not as much as during the summer.

I too debated a day or overnight trip to Barrow just to say I've done it, but it really didn't look like there was much to do besides a museum or two. Instead, I took AS143 home which went from FAI-SCC-BRW-ANC. In Prudhoe Bay and Barrow, I was able to get off and walk into the "terminal" which was more than enough for me.