I'll give you that Spock is very intelligent, but that doesn't mean all Vulcans share his intellect. Other Vulcans such as Tuvok, Vorik, or T'pol don't come across as any more intelligent than their human peers.
Later Trek has had some rather un-Vulcan Vulcans appear from time to time. The deeper you go into Trekdom the more you will find contradictions and complications.
There is, however, on-screen evidence which establishes that Vulcans, as a race, are more intelligent than humans.
Droxine, for example, is intellectually interested in Spock because of his race.
In TMP Kirk remarks that he'd prefer a Vulcan for the science station.
In TOS, the crew basically concedes that Vulcans have an intellectual edge over humans, but that humans make up for IQ with EQ -- intuition, creativity, spirit, emotional reasoning, etc.
We did witness a sort of dumbing down of Vulcans and a rather bizarre humanizing of Vulcans who had no human half to reconcile (full-blooded Vulcans), but I think it is still safe to say that your average Vulcan is intellectually superior to most other anthropoid species in the Trek verse, even if the margin appears closer than it did in TOS.