Upgrades are relatively rare. We cruise off season, and we've been upgraded once in 12 cruises. I don't count "upgrades" from a 9 to an 8 or a 12 to an 11 which are really the same cabin, only a different location on the ship.
I'm going to make a suggestion--the only difference between a cat 10 and an 11 or 12 is the split bathroom. (unless, of course, you are getting one of the secret porthole 10s) For 2 people, do you really want the split bathroom? I've found for 2 of us that it isn't a big deal, especially since I normally shower in the locker room at the spa after using the fitness center. You might choose to book a 12 gty (in which case you frequently sail in an 11 or better), or book an 11. Either way, you will save some $ which can be used for fun. Alternatively, book a 9 so you'll have the porthole. It is just personal opinion, but for the 2 of us, I find a 10 to be a "not worth it" category because the split bath isn't an issue. For more people, it would certainly be a benefit.