If you don't need to plan your vacation several months or more in advance, and aren't picky about stateroom location, then GT rates (forvthe general public), military rates, or Florida resident rates are the way to go. We've sailed GT twice and gotten respectable deals. (Not really good deals, as this is still mega-overpriced
DCL we're talking about.) One of those cruises was a Christmas week cruise Dream that I'd been following since opening day, but never booked as it was too pricey imo. I noticed the ship never seemed to fill up (GTY availability indicates fill-up), and then a few months before the cruise, GT rates opened up and we nabbed one. Got a verandah for cheaper than an inside was on opening day. That said, it still wasn't cheap or comparable to other lines in terms of cost.
One issue with GT rates is that you cannot choose your stateroom, so if you're at all picky, forget about it. I've seen people whine about the GT room they got: "Why would they put a couple with a baby over a nightclub?" Well, if you're GT, they'll put you wherever they have space. However, DCL has very few "bad" rooms.
The other issue with GT is that they don't show up for every cruise, and there is no way to know for sure when they'll pop up or how long they'll be available. So you need to be able to plan for the cruise just a few months before, and be able to pay for it all at once.