Always book what you want, don't hope for an upgrade.
We booked category 10, and the week before got upgraded to category 6. We moved from deck 2 to deck 7 and gained a veranda, otherwise the rooms were identical.
Was it nice? YES. Would I pay $1500 it would have cost me to get the verandah, NO. We did spend more time in the cabin because of the verandah, so missed more stuff on the ship. Never found time to swim on board.
My wife and I have been on 6 cruises, she insists on a porthole, while I could deal with an inside.
DCL was the only line to upgrade us, and the only line we had a verandah on.
Only downside to an upgrade is, we got our cabin assignment when we booked, 11 months in advance. We did all our homework based on being in that cabin on deck 2. So some of that homework was a was of time, because everything we planned was based on going up xxx number of decks, and except for Topsiders and the Pools, almost everything on deck 7 starts with going DOWN xxx decks.