There are plenty of lousy hotels in MB, but Dunes Village isn't one of them. We loved it at it's grand opening, and we'll be headed back there soon! (We also like the Caribbean Resort and Dayton House, but Dunes Village is our favorite so far.)
We generally go low-budget and spend most of our time on the beach and in the pools. No shows, shopping, etc. I usually do take DD to the Children's Museum once each trip, on a rainy day (we go twice a year, except I wheedled everyone into accepting Disney World last time instead of MB).

I think the Children's Museum is overpriced for what it is (you can usually find a coupon in a local parents magazine), but that's the beach for you. It's not the biggest place (most of the exhibits are in one big room), but DD4 always enjoys it, and there is a seashell exhibit in case you want to review what you might be finding on the beach on a lucky day.
We also usually splurge on one dinner at the Sea Captain's House. Nice ocean view, decent seafood.
I think the 2 Dunes Village buildings aren't that different, since the whole resort is so new, even the "old" part isn't really old. I think they just have a different mix of room types. Both buildings will have plenty of pools, indoor and outdoor stuff, etc. When we were there at grand opening, the 2nd building was under construction, so we got a look at it going up. I'm sure if you call, they could give you a little more info, if that is of concern.
Good choice you made!
