A really quick and rushed plan, but here is what I have in mind:
So, the pink lines represent the main and secondary path into the new area. The carpark north of expansion would also be expanded to accomodate further guests, and two paths from the old section of the car park and the expanded car park would lead onto the lower end of the new area.
The large brown structure either side would form the main entertainments complex. It would contain a large cinema, presented by Merlin themselves, or Cineworld/Odeon etc. I am thinking of this on the upper half of the south structure. On the upper floor, would be a large bowling alley and entertainments complex, containing a large arcade. All of this could be Merlin branded with a dash of Towers theming. To connect the south structure to the North structure, would be a large sky bridge crossing the main path which sits below it.
In the North structure would be the more teenage/adult aimed building, with the exception of the first floor. The first floor would contain several shops, either in house Merlin ones or retail stores you'd find on the high street. The second floor would contain a large bar and night club, aimed at the older guests staying on the resort. A glimpse at how it could look:
The main path leading inbetween these two structures would contain grass islands, much like the ones found on Towers Street in the park. The contents of the grass islands be it flowers, trees, small fountains or even more frogs would be the resort's choice entirely. At the end of the main path, is the park's third hotel, with the largest restaurant of the resort on the first floor. The circles infront of this would be some fancy fountains of some sort. I imagine it to resemble this style, but shaped to fit the footprint:
Obviously there is more chance of myself becoming prime minister than this ever happening on how I visualise it, but we can dream, hey?