This is like the hottest thread in the history of the NPD forums. Or at least in quite some time.
I think the OP asked a legitimate question. I have absolutely no strong beliefs here. This is an empirical question and the only way to answer an empirical question is with data.
Here:
http://www.ioe.ac.uk/research/98820.html
This study did not find much of a link - in fact the only link was between narcissism and lower non-verbal intelligence.
In my own case, my full scale IQ is 146, and my verbal score is very high, but I have some sub-scores that are barely above 100. And my emotional intelligence? That can't be measured, but if it could I would probably be average or below average.
So the left hemisphere of my brain is supercharged. The right hemisphere? Not so much. IMO the cognitive side of my brain "takes over" for what a normal person processes emotionally. And when your brain does this for a long enough time the connection between your right and left hemispheres starts to diminish.