Instead of winning a raid based on who has the most power how about once a raid is formed each side is given a list of objectives they need to finish in order to win the raid. For instance: there could be something like; Complete 500 attacks against a level 50 npc, or gain 1,000,000 credits, collect 5 bounties etc. These objectives could be shared among members of the guild so that instead of 1 player doing all 500 attacks 2 players could each do 250 attacks to achieve that objective.

These objectives would get harder depending on how strong the guilds involved are, and they could also be random so that each guild might not have the same objectives. This idea could also carry over to regular boss raids but would need to have somewhat different objectives to prevent 1 person from taking out high level bosses by themselves.

Also, seeing as how the difficulty of the raids would increase the rewards should increase also, perhaps even have prorated rewards, meaning your reward is based on how much of a contribution you made to the raid.