I myself have only gone about half way through MC. I gotta tell ya other then visually, the instance isn't what I would call fun. However that being said it might be kind of cool to do it maybe one last time. I say one last time because as rumor has it. In the Lich King Molten Core will be changed and will become a lvl 80 raid instance. Not sure if thats true or not.
The good news is I dont believe everyone has to get attuned for MC. I heard that warlocks can now summon directly into the instance. Even those who are not attuned. So only 3 people would need to get attuned. Warlock and 2 to help summon.