DWI enforcement guru here. I have never lost a case whether the offender was completely cooperative or outright refused everything.
I can usually tell if if I have a drunk by approaching the violator, asking for DL and insurance, having him sit in my patrol car, and talking with him for about 10 seconds. So, you can't legally refuse to do those things, yet I can ollect a HUGE amount of evidence from those simple acts. How do you think we gather evidence when the drunk is laying on a stretcher after a motor vehicle accident? As much as defense attorneys have attempted to spin it, you simply do not have to have sobriety tests to get a conviction.
Once the officer has a decent history of DWI arrests/convictions, basically, you can get a lot of convictions by simply clearly articulating your observations of the offender's eyes, smell, movements, speech, etc. These are usually very subtle, but obvious when you have experience.
99/100 drunks are NOT like you see on "COPS" where they are falling all over the place and puking. That goes into another topic all together...in-car video cameras. These were sold to many departments as primarily DWI enforcement tools. They are only tools for the defense. Why? A untrained jury will see a person on tape that DOES NOT look like the "drunk" they have in their mind from watching COPS and other TV shows. Therefore, they must be sober...
A good defense attorney will get the tape from the traffic stop and try to get a jury dumb enough to make a decisoin based on their ignorance of what a real drunk looks like.
As far as sobriety checkpoints, if there is no evidence of intoxication from the inital contact(see above), you will not be asked to do sobtriety tests.