Where to have the tournament is a tough question. I'm not at all convinced that St Paul guarantees better attendance. I was at last year's tournament, and attended most of the WCHA tournaments over the last 13 years. The WCHA tournament attendance was really boosted by North Dakota (whose fans travel extremely well), St Cloud, Duluth, and even Mankato. Frankly, once MN loses, or when they are not playing, the attendance was noticeably weaker. It was really easy to spot in years when both Denver and CC made the final 5, and the Gophers were not playing/lost (despite the ridiculous Red Baron announcements every year of a "new" attendance record).
Love the Excel as a venue; but, it's a long way to travel for 4 of the schools, so I just don't think it's ever going to draw like the WCHA did unless the B1G does expand westward (Nebraska, Iowa). As far as Detroit, I think it will be interesting to see how many PSU fans travel there this year. That could actually prove a better atmosphere if PSU can bring a decent contingent of fans.
Personally, I'd like to see Chicago tried for a couple of years - slightly more centrally located, a more touristy destination for those who want to lock in a trip/have to travel further. I know it's tough to get the casual fan with everyone focused on the basketball tournament; but, it is more centrally located and there are a lot of alumni there. Assume the Chicago venues have sports bars in them - maybe show the ball tournament on some of those TV's in the stadium as well as the hockey as cross-sell as a viewing party/combo to draw some people in.