The rooms increase "Films sold". The girls get more stamina in better rooms, so either films ARE exp for the girls or the exp is increased too, but this fact is not written on the buy tag for the rooms.
The numbers would be in the right area. Currently waiting for Lola in room 1. She has two pos and with one I get a lvl of stamina with the other position not. And I have 218/563, so with the 500 mentionend, that would be a lvl up. Will check later the number of films sold and the new lvl up requirement.