I think it is the exact opposite:
An understanding of philosophy does not influence intelligence, intelligence influences understanding of philosophy.
It has always seemed to me (from my views with it) that intelligent people are drawn to philosophy, perhaps merely out of the fact that they are more intelligent and thus more easily grasp the concepts. I don’t think philosophy will make you 15 IQ points higher than your peers, I think the fact that your IQ is 15 points higher than your peers will draw you more towards philosophy. Philosophers and philosophy students seem to generally be more motivated, goal-oriented and merely capable of more complex though than most other disciplines… but I think this is the appeal of philosophy not the result of it.