First off, I do like this game! Great style and fun co-operative gameplay. My thought is this:

Everyone should always get SOMETHING for their time. I feel both Raiders and Antagonists should be rewarded with partial reward (gold/exp/etc.) but not drops or anything of that sort even if they do not succeed. Make it based on their progress/performance and people will feel more incentivized to play all modes and stick around to the end.

Thoughts?