Well, boost over what you'd get if the Earth didn't rotate at all. But the closer to the equator you are, the less fuel the rocket requires, which is certainly advantageous. When NASA was considering launching from California, they had to design fiberglass booster casings to reduce weight and make up for the lost rotational speed.
The political bit would be Johnson Space Center in Houston. There's already a control facility in Cape Canaveral, so the Houston space center really wasn't worth it: just an extra few million in personnel and construction costs, plus shuttling astronauts back and forth. (Canaveral handles launches/landings, and Houston handles the rest... but both are capable of handling the entire thing). Johnson Space Center was mostly created because Lyndon Johnson is from Texas.