I'm seeming to find out that an upgrade is more likely when one is guaranteed a minimum category rather than when one is assigned an actual cabin number. At least that's how it has been working out for me. Does this seem plausible?
I don't think it really matters on Princess since unlike most cruise lines you can book a cabin number and have it marked that you will accept (or not) upgrades. In face the last 2 times I sailed Princess, one time I had a cabin number and was upgraded, the time I had a guarantee I got a room in the category I booked.
I finally decided to not agree to a possible upgrade, because we have a category AC with larger covered balconies and I didn't want to take a change and be upgraded to a balcony that is uncovered. The upgrades are done by computer and if you are not happy you could be out of luck. trying to get a better location. There are 4 other couples with us, that have decided to roll with it and see where they go. We all have assigned cabins.
If you are happy with your cabin and cabin location, I'd do the same and just keep it and turn down any possible upgrade too. Next cruise we have an assigned aft balcony cabin and I also want to keep that one for sure, enjoy your cruise!