I'd like to see a more thorough emissions test be implemented (i.e. more than testing at two speeds, enough to gauge all operating conditions) so that it could be more objective in its process. This would also have the benefit of allowing a way to bypass the restrictive modification exception system.
1: http://www.theguardian.com/environment/green-living-blog/201...
For instance, my fun car had a persistent miss that made it basically undrivable. It took me something like 20-30 hours to find the issues and fix them. I have OBD2 scanners (the real deal, not the toys), all the tools needed, and the ability to read the service manuals and follow the dianostic proceedures.
Someone driving an old pile, isn’t likely to have the time, know how, or funds to fix the old car. So instead of spending $5k to fix the thing, they spend $300/mo on a new (or new to them) car.
You can see a lot of details here. http://www.rff.org/Documents/RFF-DP-99-23-REV.pdf Also, repairs often increase fuel economy so not only do city's become far more livable again the net cost is fairly low.