Yeah, I think they make some allowances just to make interesting episodes without really worrying too much about what would really happen.
As for the engine thing, there was one episode of TNG where they fired the impulse engines briefly, and then tried to drift out of some asteroids, with only the occasional thruster burst for course corrections to avoid collisions. In that episode, they had slight speed variations due to gravimetric effects from the nearby large asteriods/meteors. But other than that, they stayed drifting at the same speed even with their engines off.
Btw, anyone know how their impulse engines are supposed to work? I've sort of wondered what exactly they are. Is it supposed to work a little more traditionally like thrusters do? Or is it supposed to be more like an extension of the warp drive only at slower speeds? Probably not the later though, since they can have one without the other. Too many episodes where they lose warp drive, but still have impulse power. Hmm, maybe it's just some way of transferring engery directly into kenetic energy uniformly throughout the ship. But then what about inertia dampners?
Gah, I think you've got me thinking about this too much now. It's just a awesome TV show that's fun to watch. Doesn't need to be real.
