Yeah that was my thoughts as of now too was there wasnt that much movies out there that utilized 7.1 thats why I havent pulled the trigger yet and go for 7.1. My set up now is the BPX are on the back wall behind my head. I was thinking bout putting the 350's next to each other directly behind my head, but once again wasnt sure if that was even needed for such small room tho.
If your side surrounds are already on the rear walls, then I'm pretty sure 7.1 is not for you. By going with 7.1, assuming you have the proper and significant space behind you as a listener, you are then more free to put the side surrounds at 90 degrees, because they no longer have to try to straddle for the side and rear areas.
IMO, 7.1 is worth it, if you have the space. My rear speakers were only like $200, maybe less. There are currently 193 bluray titles that are recorded in 7.1, and the last 7.1 movie I remember seeing, Toy Story 3, had some of the best audio on a movie I've heard to date.
If you have tall ceilings with money to burn, you can try height speakers for a taller soundstage. If you have plenty of width (and you don't mind the actual speaker placements), you can try Audyssey DSX widths too. There are extremely few processors that can do the simultaneous 11.1, many more at 9.1, and of course just about all of them can do 7.1.