I am in Victoria Palms in Donna, TX which is a mid valley location and one of the highest priced parks of the 400 mentioned in the RGV. I started wintering here as a winter Texan in my RV 13 or so years ago. At that time you needed a reservation months in advance and the entire 1,000 plus sites were rented for most of the winter season.
The park has mobile homes, park models and RV sites along with a 100 three room suites and 20 motel rooms. The RV sites are divided between an older area with small sites and a newer area with large landscaped sites.
A number of years ago the reservation requirement was no longer needed and about three years ago there were many unoccupied sites in the winter season. The last two years has seen a reversal in this trend. Although reservations are still not needed, if you want to be in the new and nicer section you will need a reservation. Last year this section was fully occupied.
Regarding the question "what is there to do"? My friends in NJ ask me this all the time. My first answer is the resort is like a cruise ship that never moves. We have, shows, dances activities, pools, a restaurant, etc. My second answer is that this is not a dirty dusty backwater in the middle of nowhere. Current estimates put the American side of the RGV population at 1.3 million and the Mexican side has over 2 million. There is plenty to do.
Prior to my coming to the RGV I wintered in Florida in the Orlando and Vero Beach areas. I found out that I did not want to go to the Orlando area attractions every day. How many days can you spend at Disney or Universal before you are theme parked out? Vero Beach is an up scale Florida area and very nice.......... but guess what........ there is more to do in the RGV than in the Vero Beach area.
I do not know if the trend in my RV park translates to the rest of the parks in the RGV. What I see is that the people in my park want the best sites and they make use of all that the "criuse ship" has to offer.