It's probably been brought up by others, but in general, if there's a better room you'd like, and you're in the days past final payment so pricing has come down, give them a call and ask what it would cost to get the nicer room outright. Sometimes it's less than the lowest bid pricing!
There is a caveat- NCL won't let you upgrade to a room that's less than the price of the room you already paid for. So if you're in a standard balcony room that you paid $3k for, and the pricing for a Haven room dropped to $2800, they won't let you upgrade to it, even if you tell them to keep the extra $200. The room you're upgrading to has to cost more, even by a tiny bit, than your original room.
Overall I don't think the bid process is a good idea but, 23words got a phenomenal upgrade through bidding! And by getting the Haven Aft (stayed there, it's a wonderful room!) they even avoid the dreaded Epic bathroom configuration that polarizes people so much.