Rachel,
How about if you use your stash for backings for quilts as you go along? If you tend to make a certain size make up a couple of backings to have ready. then the next time you finish up a quilt the "after the flimsy" portion will go along much faster!
I hope you find a way to become comfortable with what you have already purchased and have a stash. Noone should feel the guilt over the gluttonous way in which I purchased fabric these past 20 years.
denise/deBRAT holding down the tampa bay area with the weight of all my fabric