Well, I wasn't going to step into a manufacturers board, but since you haven't received any thoughts on the matter I'll give my $0.02:
Go full range in the rears. By all means, absolutely.
What you may consider wasted money on seldom used content, well.... We've all wasted money on the small stuff haven't we?

I don't know exaclty how much you're talking financially for Salk rears, but I'm sure they're not the kind of speakers you'd buy without putting some thought behind first. You've got a nice HT room dude, Rear content can be pretty exciting stuff when you're getting everything they have to offer. If you aren't getting everything then you're selling yourself, and your room, short.
I say go for it.
Bob