I have a strange idea :
Why not create a collectible subtheme for harry potter like Ninjago ?
May be Quidditch subtheme ? With cards and rules to play with your friends ?
I propose this :
Team pack or duel pack
4 figures, some accessories
Price 12.99$
Booster pack :
Boost your team ! Collect the 10 figures from Harry Potter Quidditch
Each packet have 2 randoms minifigures !
Price : 4$
Hogwarts Quidditch pitch :
Play your own Quidditch match with your friends here !
Madam Hooch, Lee Jordan and spectators
Price : I Don't know really
What do you think ?
Oh and for regulars sets I just hope some battlpacks to make a real battle for Hogwarts !
And a "Battle Over Little Whinging" set for this : http://images.wikia.com/harrypotter/images/3/3b/Vlcsnap-2010-06-29-01h14m33s160.jpg