Having traveled west through MN on 94 for several years to get to ND for duck hunting, I can tell you without question, do not EVER let the number of ducks on MN water holes be a judge of things to come. If I did, I would turn around every year.
Sounds like this year was about the same for 6 of us as it was for you. Hunted hard for a few birds. Feast or famine really, two of us got skunked one night and only two ducks one morning. Otherwise two guys would usually get 5-6 ducks am and pm. We got access to a field where the snows and blues had been the prior two mornings. We aren't equipped for field hunting so we threw out what we had into cut barley and tried to hide as best we could in cut corn. They came back that third morning but always were about 100 yards out of range. We did manage 6 of the blues and one lone greenhead bit on our spread of mostly mallard water dekes and a dozen canada geese. What a blast watching them come in. With duck hunting being such a surprise sport, and having never field hunted, i never get any adrenaline rush but when that first flock appeared and looked like it was coming right for us and I had 10 minutes to watch 'em come in, I had a rush just like waiting for that deer to present a good shot. (on the fourth morning, the geese went elsewhere entirely)