It has been the experience on the boards that if you have requested adjoining or connecting rooms, either both rooms are upgraded or neither is. That's not a worry for you.
Horace is right--you get an upgrade either because they were able to sell your room to someone else at a higher price or because someone in a higher level cabin cancelled at the last minute and the pixie dust landed on you.
The bottom line, as always, is to book a cabin where you will be happy. If you get an upgrade, it is wonderful, but do not book low counting on an upgrade (either free or at port). It is really not very likely to happen.