First of all I don't believe any raid system should be a part of the RVR. The defending port should not lose a large amount (if any) of its investments, and there should be a limit to how often a port can be raided.
Secondly, the raiders should be compensated for a successful raid regardless of whether or not they make it back to home port. Like one or two ships with the port's bonuses to share amongst the raiding group, or some other prize. This would get more smaller groups/clans/nations involved in the raiding system.
Like others here, I believe that unless this new mechanic is handled very carefully, it will end very badly. Too many players seem to enjoy ruining the game for others so ANY way a new system/mechanic can be exploited to grief others WILL be put into use.