I would make blast markers able to affect troops in an open top vehicle if the centre point of the blast marker is within the vehicle otherwise the sides of the vehicle protect them from the blast. The current rules make no sense and make open topped vehicles which are cheap too effective unless you have template weapons. All Psychic powers should be able to be cast (using fire points for LOS) from vehicles but add one to the warp charge required to take into account the bumpy ride.