Since Dream World is pretty much compatible with Join Avenue, I'll put them together here.
One of the best features in Gen 5 was the introduction of Dream World where you could get pokemons with Hidden Abilities.
And with people visiting your Dream Home, you get more visitors in Join Avenue (at least it's one way to get more visitors)
In Join Avenue, you could get rare items in bulks at cheap prices, and even had a nursery to help with breeding.
Do you want them to be in Gen 6?