Are you a gambler? The chances of the cruise you want going down last minute are about the same as it going up. If it sells well, it climbs. If they have trouble filling the ship, it drops. You have a double risk in waiting. It could go up AND it could sell out before you book it. If you're very flexible with what, when, how long and where you cruise, you have a good chance of finding a last minute bargin on some ship somewhere. If your choices are limited, book it and book it fast. This is especially true if you need cabins close together, any cabins for more than two passengers or care what deck you're on etc.
Waiting is a gamble, you might get lucky and you might loose your chance to cruise.
You are looking at a New Years cruise. They usually always sell out. As rooms get fewer prices go up. If you really want this cruise you need to book it NOW! Check with your travel agent. Many times if a rate drops you can get the adjusted fare. We did last year. Saved about $400.00
well here is the point:
If you are at a carnival cruise just buy the ticket and then check their site a few week before your cruise for specials on their prices, if you see that a cabin $$$ with the same category as yours get a down price just call them and they will give you the same price at that moment. So anyway you will have a great deal even when you book early.
Also remember on new years eve everyone want to cruise, even now you are late for most of the better cabins or prices, that's the time that the cruise lines sells the better so maybe is time to make that booking before is too late...