The bogus part of this, is that like the LA area, or Salt Lake, the front range sits badly geographically. 300 days a year, the air quality is tolerable for the region, and does not exceed the clean air requirements. Yes, the brown cloud may roll thorugh every so often, but, it is within the limits. However, on occasion, smog and pollution is brought in from other regions and concentrates against the mountians. This triggers the failures. Smog from the pacific NW, Chicago, Southern US and even LA can and will be pumped into the area with specific storm and weather events. Then is gets isolated and stranded over Denver.
A reduction in local emmisions will help, but EPA dinging the Denver Metro area for poor air quality on days that the smog came from a thousand miles away is stupid. Furthermore, the objective of the car manufactures of today, has been to build junk, and make you buy a new car every few years. I would really like to see the percentages of older vehicles registered and on the road, compared to new ones, and just how much polluting a small number of vehicles can really do.
Look around these cities and tell me how many vehicles you see from the 70's, 80's or even before 1990, not that many, so why worry about testing 30 year old vehicles.