Experience and Valor should reward the effort. Commendations and credits should reward the result, I think.
Kills and medals should award experience and right away - in fact in most MMO games it works that way. If you kill someone in PvE (be that a class quest, planetary quest, fp, op or space mission), you get exp right away, why should it be different in PvP? A simple change, have kills award experience, and this thread will become unnecesarry. You are entitled to your experience right away for killing something.
EDIT: A larger experience boost should still be given out at the end of the match, based on medals and mvps, but xp for kills would ensure that no one can perpetually stay at a certain level.
I would also give out valor points on the fly. Say 1 for the first kill, 2 for the second, 5 for the third, 10 for the fourth and 20 for the fifth and each consecutive kill thereafter. If you die, you start from 1 again.
As for Medals awarding credits and comms right away? No, I think this wouldn't be a particularly good idea because some medals are notoriously easy to get. (2,5k dmg, 5k dmg, 2,5k heal, 5k heal, def medals etc.) If this was the case, there would be no incentive to remain in a losing warzone once you get 8 medals. We'd see entire teams desert once they realize that they cannot turn the match around. (It is already happening to a certain extent but instant credits and comms with aggravate the issue.)
I realize that it would help people who accidentally disconnect in the middle of a match not leave empty-handed for their effort, but in the case of credits and commendations, I think the potential of their misuse far outweighs the potential of their usefulness.
I think this is an adequate solution - similar to one Doomsday presented earlier I believe. A slow leak of xp, a chunk rewarded at the end. I agree that Comms and credits right away would encourage people quitting early even more.