Party for the Senses does not sell out near as fast as the other special dining, but you do need to buy it ahead of time since it does sometimes sell out.
As for the food being the same as the resturants... at last check there was no Polish, Indian, Austrialian, Greek resturant at WDW so the only place you got those special items was the food and wine fest..... If however, you are a real picky eater... this may not be a good event.
Last time I went I used about $100 in Disney reward dollars over the course of a week stay... I was stuffed A LOT, I can't imagine even two people spending $100 and not being full in one day!