Mr Spock, being from the planet Vulcan might have stated these words: "Vegetarians are Logical". Now he can say 'Vegetarians are Smarter'.
A scientific study by a Southampton University team in the British Medical Journal reports that the average vegetarian tend to have five IQ points more than the average person.
However, the report seems to indicate it isn't the exclusion of meat that makes one smarter because "there was no difference in IQ score between strict vegetarians and those who said they were vegetarian but who reported eating fish or chicken."
This suggests to me that intelligent people tend to eat healthier and because of this they are more likely to gravitate towards a vegetarian diet. And because Brits tend to become vegetarian more out of ethics than health (the exact polar opposite to their American counterparts in my estimation), maybe there is a correlation between intelligence and empathy. I guess we'll have to wait for that study.
BBC - High IQ link to being vegetarian