I love scrappy quilts too and I used to do what you do - 1/2 yard at a time. I've decided that's just a little too small and now buy 1-2 yards at a time. That way I can lop off a piece and do scrappy if I want; OR it's usually enough for a more "patterned" quilt if that's what I decide to do with it.
At those prices I'd probably be picking up prints for backings too. I tend to make a lot of 72" square quilts as oversized throws. I need about 5 yards of a print to make a backing on those; so when I'm buying regular-width prints for backings I buy them in 5-yard increments. I especially like printed backings on quilts for kids. Quilts I make for grown-ups and for beds tend to get more neutral backings, but that's not a rule, just a tendency.
I like the fabrics you bought...but where's the rest of it? ;-) Oh, you must have some of that "self control" stuff I've heard so much about! LOL