The Enterprise is propelled by matter-antimatter reactors.
(a very concise statement)
Actually, that would probably be as far from concise as can be, as Spock is selectively describing the one aspect of the propulsion system that would be of importance to his plan of blowing up the ship. It's no different from him saying that a car is propelled by gasoline if he intends to make a big fire and has no interest of propelling anything anywhere.
Hmm...you are right but for a different reason. Since Spock doesn't make a distinction between warp and (normal) impulse drive, the logical conclusion would therefore be that the energy the m-am reactors provide equally powers the warp drive and
the (nomal) impulse drive (ahead of the TMP impulse drive concept where m-am energy is directly fed to the impulse drive!).
Looks like TNG now has a problem explaining the impulse drive of the Enterprise-D