Renfe has just announced that there is going to be a new class for long distance travel, and this is called Turista Plus. It costs 20% more than the full price of tourist class. The only advantage you will have is that you will get the wider seat of the preferente class. This will apply for travel between Aug. 1, 21012 and Sept. 29, 2012.
In my opinion it is not worth it. It is better to try to get the web discount on the tourist class seats.