The Fourth Amendment does not give you the right to drive drunk.
It seems you are missing the entire point. Behavior indicating drunk driving IS a probable cause. What is being discussed is basically a checkpoint with no probable cause which essentially is unconstitutional, again despite what the courts have ruled IMO, because it can lead to criminal prosecution without due process which may have nothing to do with driving at all. If you are stopped at such a checkpoint and a cop confiscates what he or the department subjectively claims is a large sum of money what does this have to do with driving drunk?
Now before you claim they are confiscating money from suspected drug dealers that is not always the case. I remember before Katrina some Louisiana cops on I-10 used to rob families on route to Florida for vacation using the drug laws as justification.
If you are not doing anything wrong and if there is not a matter of safety involved such as an escaped prisoner in the area for example I'm really not sure roadblocks fits the spirit of the Constitutional protection. In fact it's kinda what the law was written to prevent. Just stopping people to search their persons and property seems to get a free pass only because police have to announce them in advance. That justification is a mighty slippery slope.
I get that some feel the ends justify the means but the whole purpose of the Constitution is to protect us from the government justifying any and all means. It's no wonder some members of Congress feel the Constitution is pretty much a meaningless inconvenience to have to work around. Some act like they're never even read it once.