I've done scrappy several ways. I did a star quilt in just two colors but used 17 reds and over 30 neutrals. I did two log cabins where I sorted into light and dark and just used whatever came out of the bag. They turned out really cool and fairly masculine since I used every ugly and weird fabric I could find. I do square in a square scrap quilts for the girls where I go thru and pick each square combination. I put some together that really go together, some don't really go together but work together and some clash. Putting a few together that really clash really gives those quilts zing. For the boys I do string quilts but for them I make light blocks and dark blocks and then cut them on opposite diagonals and then put them back together. For those quilts I just made two piles of light and dark and did all of the light blocks first and just plucked strings out of the pile and then did the same with the darks.
I should write a book about how to make scrap fabrics work together.