I'm not sure I even understand what your point is now.
Public spending tries to account for quality all the time. Quality "metrics" of various sorts exist in lots of places and can always be evaluated (or found, then evaluated, as may often need to be the case) when making trade-offs.
In the case of public parking, there are ways to improve "quality" by reducing overall parking pressure at specific locations by "moving" it to other areas, such as park-and-ride combinations with public transportation, improving access to site-to-site ground transportation (bicycles, scooters, wheelchairs, segways, what have you), and just improved public transportation in general.
Quantity is often an easier metric to optimize for because it's always a number, but that's all the more reason for public spending to find ways to do the hard thing and optimize for quality. That's why we elect people to work on hard problems and care so much about public spending.