1. I thought the graviton was looking quite likely to be its own antiparticle
2. Navigational deflectors being unnecessary at warp doesn't seem supported by the show
1. I have no idea, never heard of this before.
2. I'd prefer to explain this away as navigational deflectors only being necessary under impulse power, if at all (nothing in the show actually references the nav deflector being used at warp). More to the point, the only time the deflector is referenced as being used for the purpose of DEFLECTING things is for pushing large asteroids out of the ship's path. This happens, AFAIK, twice: once in Paradise Syndrome and again in TMP, the second attempt failing because the wormhole was screwing up all ship's systems. In light of this, I'd prefer to think that pushing things around is not the primary purpose of the deflector at all; if it was, it would kind of suck that by the 24th century most starships prefer to push asteroids and comets with tractor beams instead of the giant deflector dish which is supposedly custom-built for this purpose.