First of all, welcome to Flyer Talk -

Regarding MSP, my hometown, if you are interested you can take the light rail to the Mall of America which is only about a 10 minute ride. Estimate $2.50 possibly less depending on time of day.

Tons of restaurants, most are chains...personally I'm not a shopper so MOA isn't of interest but I bet you can find model planes somewhere.

I've never been to the observation deck at MSP so can't answer your question. I happen to like Ike's restaurant and French Meadow Bakery but there's a Chili's and a couple other chains as well. Also Wolfgang Puck.

Hope this helps a little and enjoy your layover.