Skip the Hard Rock. The food sucks. Go to Mickey's Diner in downtown Minneapolis. It's more authentic Twin Cities and the food is actually good. What your talking about is St. Paul. Minneapolis is a different city. The light rail goes through Minneapolis
The Children's Museum is just across the street...if you happen to have anyone under the age of 10 or so traveling with you.
Take a tour of the capital if you can...it's not far from there.
Find somewhere to have a Jucy Lucy. Pizzaburgers forever! We used to get them at a little drive-in over on White Bear, but it's long gone!
As for the zoo, if you're a member of your local zoo, check to see if it's on the reciprocal list. If I remember correctly, it wasn't the last time we were there, but things change. If you go, be sure to check the show times for the dolphins so you don't miss them!If I'm remembering right the zoo costs $14 per person and an additional 10 to park. Go to the Como Zoo in St. Paul
If you go to Mall of America, go down into the theme park area and look for the plaque for home plate from old Met Stadium! Personally, unless I had small children or money for a shopping spree, I'd skip the mall!
Do you know anyone who lives in the Twin Cities? If so, they can check out a visitor pass from the local library. It allows up to 4 people into various venues...they change from time-to-time but include museums and the zoo...for FREE! I don't know if out-of-town visitors can get a library card there to use this...you might call one of the libraries to find out.
If you're interested in free concerts in the park...the start in May...search for the Minneapolis Parks and Rec Board. They have free concerts a couple of times a week at various parks around the area.
I miss going to the Twin Cities. I lived there when I was young, then spent most summers there while I was in grade school. I visited regularly up until about 5 years ago. Sadly, my aunts and uncles who lived there have all passed away. It's a wonderful area to visit!