In Denver, there are lots and lots of good places to eat. Casa Bonita is NOT one of them. It's fun, especially for kids, and their sopapillas are outstanding, but as Mexican food goes, CB's is at the bottom of the barrel.
In the Denver area (not in Denver), the Coors Brewery in Golden has a neat tour. A day trip through Estes Park to Rocky Mountain National Park is outstanding. The Peak to Peak highway is a nice day trip, also--takes you through the weird little towns of Ward and Nederland. If you're into bird watching at all, go to Barr Lake and watch the eagles--you need binoculars. Farther south, take the cog railway up Pikes Peak--that's a fabulous ride--or take the Georgetown Loop railway west of Denver at (of all places) Georgetown--which is incidentally a fascinating little town to wander through.
If you're interested in gambling, the towns of Blackhawk and Central City are not all that far from Denver. Central City has some fascinating history--home of the face on the barroom floor, Baby Doe Tabor, Unsinkable Molly Brown, etc.
In Denver, if it was later in the Spring, I'd say spend some time at Elitch's, a first class amusement park. If you want a nostalgic amusement park, Lakeside is one--takes you back about 60 years. There's the Forney transportation museum. There's the Wings Over The Rockies aviation museum, which keeps getting better.
Just some ideas--I'm not much of a Denver booster--it's just too darned big for me.
Cary