I suspect it is about as popular as it is going to get already. The drug is available now.
Cops would not just have to worry about drunk drivers, but hordes of stoned drivers as well.
There is a point to be made that police would need new tools to ascertain impairment. But I don't believe that the status quo will change that much. Those people who want to smoke pot and go out cruising already are.
One could argue that the number of drivers may go down, as legality negates the need to be on the open road where the fumes don't cause suspicion.
You may not have done so, but many advocates say that decriminalization would "take away the profits of the crime syndicates." Actually, overall profits could go up, because consumption would increase. And who's to say that giant co's like Coors, Anheuser-Busch, etc. wouldn't go into the business?
More power to'em. I would rather companies than crime syndicates run the business, and I have no philosophical objections to capitalism.
SD
We are stuck with alcohol. It's been part of every culture for thousands of years. In fact, there's evidence some ethnic groups have evolved the ability to handle it relatively well. However, it's still a multibillion-dollar health and social problem. Once other drugs are legalized and go "mainstream," I think we will see that problem multiplied.