Not sure if this is going to be much help but...
Four cruises; so obviously no good status with anyone yet. Two moderate upgrades on our 3rd and 4th cruises.
1. Celebrity Millennium, Alaska. Booked the cheapest inside cabin we could get our hands on. Upgraded to an outside cabin. The only quirk was that we were near the front of the ship a few cabins away from a door that led into a technical area for the theater so there was a bit of traffic. The cruise was one of the first of the season so I think they had trouble selling out the cruise. I'm guessing they oversold the inside cabins just to grab pax and just upgraded whoever.
2. RC Liberty OTS, W Caribbean. Booked an inside guarantee via our travel agent. Somehow we got upgraded to an inside Promenade view which was nice. (Don't think it was our TA that got us the upgrade as she was on vacation leading up to & during our cruise and we had to deal with her backup for some issues.) Again, this was for a December sailing which I'm guessing wasn't full.