We took our son there this summer ( well I should say I did, as there was no way we were bringing all 5 of us on the flight! ) I agree with the above poster, I wouldn't recommend staying near the GDC

Although there is a fabulous calazone place just around the corner that you could eat lunch at ( it really looks like a hole in the wall resturant but man does it have GREAT calazones!!!)
I rented a car at the Denver airport and stayed in the La Quinta Denver Airport so it was about a 25 min drive in the AM due to traffic to get to Colfax but not too hard to find and I managed to get there without hassle both days, although its street parking so sometimes you have to drive around a bit to find a spot near the GDC carriage house.( and have to look closely as its really tucked in behind a taller older apartment house/building.
We didn't go to any area attractions because we used to live a few hours away in Colorado Springs in prior years so we had seen some of what Denver had to offer then, plus DS was much more interested in the hotel pool! I would recommend the Denver Childrens Museum off the freeway, it has a huge park right beside it as well and the aquarium is next to it ( although its not a huge one, its ok )
We had a great experience there with them those two days, and DS loved every minute of it! I hope your time there goes well!