The only reason I could see why they wouldn't bring them back is probably because they don't want R/S/E to be too overshadowed by D/P. I mean, sales for R/S would really decline since people could buy the game that has everything the other games have and more. I mean, with that whole trading over the Internet thing, I'm sure we won't have to do too much trading with the other games.
Personally, I kind of liked the contests. It just kind of gives you a little something else to do. *Shrugs* They can improve them or not, personally I like them as they are. Who knows, maybe they'll come out with something completely different to replace contests.
Edit: Woo! Moved up to Mineral trainer.