30+ stays at WDW resorts, since '99....only twice has anyone in our family received an upgrade. First time was at the CR...we booked a standard view, facing the parking lot, North Wing. We ended up in a lake view room...not sure how that happened. It think our TA may have had something to do with it.
The second time was part of the Year of A Million Dreams promotion. Dh was at the YC as part of a business thing....the whole group was staying there. My dd and I were across the lake at BWV, youngest dd arrived with dh (on his reservation). She moved to BWV with us for her 3 days there, and returned home with dad for school. BUT. when dh checked in at the YC??? The CM said to wait just a minute, he had to check something out. He came back and said congratulations!! As part of YoAMD, you have been upgraded to concierge!!! Are you kidding???? The only one in the company!!! So, we got to check that out.
But other than those two times? Not once. While many people here say that it happens all the time, in all reality it doesn't. The DIS boards are a very small, even miniscule, part of the WDW community. So, even if 50% of the posters said they had been upgraded??? It would be a very small percentage of the total number of WDW guests.
Disney usually upgrades for reasons of their own. Yes, it provides magic for the guest, but Disney seldom does anything out of the goodness of their hearts. There may be some maintainance issues with the room, or they may have overbooked.