Hi, and thanks for planning to stimulate the local economy!
I live in a southern suburb of Denver. I really don't get into downtown too much anymore, but used to work there and still visit occasionally. Where are you staying? Will you have a car?
There is a pedestrian mall in Denver, called the 16th Street Mall. The street is closed to cars, but there are free busses that run up and down, stopping at every cross street. Just hop on and hop off when you need to. There are lots of shops and restaurants along the mall, some are really cheap, touristy things, but some are nicer. Two small shopping centers, the Tabor Center and Denver Pavillions have nicer stores, as does the Larimer Square area (Larimer Street between 14th and 15th Streets, I think). Pavillions has a movie theater, too.
I second the Molly Brown House as a good place to visit downtown. It's an interesting tour. The Brown Palace Hotel is also worth a look. It was built in the 1890's IIRC, and it's beautiful. I believe they do high tea there (go to the website to be sure). The Ship Tavern in the hotel is a nice place to sit and have a drink.
I think of the downtown area as very safe, especially if you stay in the 16th Street Mall area. The Brown Palace is just a block off the mall at 17th Street, and I would have no problem walking there from downtown hotels at night. The Molly Brown House is within walking distance, but off in a more residential area of downtown. It's not unsafe, but less people would be around, so personally I probably wouldn't walk there at night alone. Just take the normal precautions you'd take in any city and you'll be fine.
If you have a car, the mountains are beautiful. You may be here when the aspen trees are turning, and a drive into the mountains to see the brilliant yellow colors is just gorgeous.
Downtown, there's also a nice acquarium, the Colorado History Museum, Denver Art Museum. There's a doll and miniatures museum, but I believe you'd need a car or cab to get to it. Hmm, what else are you interested in? What do you like to do?