[NullAshton]

Matter-antimatter engines are only used for warp drive, and are simply not used for impulse engines. Impulse engines use fusion generators, which also serve as secondary power in battle. Helium exhaust! Q is plot device, and doesn't mess with stuff that much, so I say leave him in there. And timetravel is just plain funny, and serves as a good excuse to revisit yesterday's enterprise. Besides, I like that episode where the Enterprise-D is stuck in a timeloop.