Simply put: There is no advantage to regulating CO2. By regulating the other pollutants there will be achieved a reduction in CO2. For example: By lowering the speed limit in the Houston attainment area there will not only be a reduction in NOx but also a reduction in CO2.
Contrary to what you may say, the State of Texas does do cost benefit analysis. Care to guess who is not required to do a cost benefit analysis? Care to guess who steps in should the state not achieve their requirements.
I'll guess, I'll guess, Question 1: EPA (actually court upheld that in most cases a cost benefit analysis is not necessary in setting health based air quality standards - wish I had a reference at hand). If Texas chooses to implement CO2 reductions within the bounds of it's legal framework it has every right to without the Senate approving the Kyoto protocol.
Question 2: EPA, and other federal agencies. The big question is how much federal highway money does Texas collect, and what would happen without it?
While GHG emissions and "global warming" are generally a different subject than ozone non-attainment requirements (federal), the fact of the matter is that pretty much anyone has the opportunity to petition executive branch agencies for action. Whether or not the agencies take that action likely depends on the general political atmosphere and specifically the political clout of the petitioning group.