Same thing here... booked our March 16 wedding cruise back in June... and last weekend they had SUITES going for over a hundred dollars cheaper than we paid for our INSIDE cabin guarantees. NCL gave no upgrade, on board credit, etc. Nothing. Even our guarantee cabins were assigned at the category we guaranteed - no upgrades on the guarantees (ship is not full). So we didn't win on gambling with guarantees.
This price drop occurred after our final payment was made, and I understand that is how NCL is. We had seven cabins in our original booking, so not quite a 'group' since not eight cabins. However, they did offer to give us some upsells for a price... Fortunately for our friends who are procrastinators, they were able to take advantage of the great deals since they had not previously booked. They all got suites for cheaper than the inside cabins my family booked.
Oh well - we'll still have a great wedding anyway.