[El_Phil]

Hyperspace is shaky, partly the theoretical existence is very much conjecture. More seriously getting into a 'higher level' dimension whatever you call it would be tricky. More tricky would be getting back to the one you came from.

Wormholes could, maybe be used for backwards time travel depending on layout and a variety of other things. This is a bad thing and so travel through them would be impossible, ie they'd collapse as soon as you try and use them. If your wormhole is so arranged that you don't time travel it has more chance of working.

On the grav plating, the density gets ridiculous. As in 1.5E9 kg of mass beneath 100mm beneath your feet will give you ~1g. In real numbers thats 1.5 million tons of material compressed so much the centre of this mass is 0.1m under your shoes. I think you'd agree the density starts getting ridiculous. There's also the point that is unidirectional and falls off with distance. So if it's just at the bottom then your upper decks have much lower gravity (it's a squared law so double the distance and the force drops by 4.). If you have plating per deck then the crew will be attracted to the ceilings, not as strongly as too the floors, but enough to be very disoreintating and bad for the body. Imagine being weakly torn apart all the time.

Gravitons... It's a logical extension of quantum mechanics so they probably do exist. Probably. But they're only 'messenger' particles, you need the source of the gravity for them to be created, so they don't really solve the problem.