There is also Miller Motorsports Park http://millermotorsportspark.com
... Definitely could handle the crowd, vendors, etc. World-class road course. No drag strip though. Might be pricey to rent out... lots of events there. NHRA sanctioned strip is at Rocky Mountain Raceways 20 miles away. The local SCCA uses RMR as one of its venues for autox.
Also... Las Vegas Motor Speedway http://lvms.com
Can't help but think there would be something in Denver as well.