WoW and SW:TOR has a small and large party option for their dungeons. What is wrong with options? I think some people here are just elitists that don't want 4-man groups doing content they had to have 8 people for.
You can either scale the difficulty back and lower the reward % or keep the same difficulty and same reward %. Risk = reward, not party size = reward. If a 4-man group can kill the same difficulty Ifrit hard mode just as well as your 8-man, then maybe you 8-man groups should pull up your big boy pants.