Let's step back for a moment. Perhaps the human race is not getting dumber. Even still, I severely doubt it is getting more intelligent. And perhaps this shrinking brain has nothing to do with our intelligence, in which case it's still entirely possible we are getting dumber.
Evolutionarily, I see no reason humans, as a species, would be development more individual intellgence. Our means of survival has become less and less individualistic essentially since we "began", and has accelerated in the direction as time has progressed. I repeat that the brain is expensive, and you don't keep what you don't need. So you might be right, maybe we're shedding the parts we don't need. Look at how things are going, those parts seem to be our capacity for solitary survival. We don't need those.
Any of the creatures on earth that have comperably populous masses, or acute division of labor (and there are few) are generally not regarded for their intelligence. Nearly all of them are hive insects. I suspect if every termite worker were a genius with an invidiualistic streak, it will hurt the species more than it would help. This approach was apparently more effective than other approaches, or else it would not have evolved. I simply can't fathom a reason humans would continue to develop all purpose intelligence at an individual level, given our current arrangement.
And as for our technology, that has little to do with cognitive skill, really. You could attribute most of it to written language. It was made possible only by our ability to preserve and send information. Now it appears that sets us apart from other animals, but I doubt it has improved much since we first developed it, and I doubt we suddenly had a click in our brains that granted us the ability to do it. I figure if, by some genie wish, you wiped the capacity for literacy from the human brain, we'd be neolithic people in one or two generations.