It's not that popular but some people cruise back to back on the same ship twice. Double the length and a bit more relaxed as if you miss something you can do it next week, or repeat things you enjoyed the first go round.
Might be an option to consider going 14 nights. Or a bit more complicated would be to do Oasis one week and Allure the next.
11 cruises in 2012, 90 nights at sea visiting 15 countries
8 cruises in 2013, 56 nights at sea visiting 7 countries
Next cruise: None scheduled
PM me if you need a cruisemate for any Europe, transatlantic, or Panama Canal cruises
Date, ship, cost pp