I think this is an oxymoron.
Now I know that intelligence varies in people more than types, however when people say there are stupid NTs, I just don't understand how that is possible.
The very personality characteristics of an NT are either developed through growing up as an intelligent person, or having NT characteristics would build a foundation for intelligence. Basically, there is no way someone could hold strategic thinking mind set, with out it leading to some type of knowledge.
If people chose to act stupid, that is a whole other story.