I don't pre-wash. If there's a color I suspect might bleed, I test a small piece in a glass of water to see if dye runs, then rub the damp fabric against white fabric to see if dye transfers. Saves me a lot of time!
Regarding shrinkage, it's true that fabrics can shrink a lot when washed. However, after a fabric is quilted closely in a quilt sandwich, it is the batting that controls shrinkage. Meaning, if a fabric would shrink 8% if washed by itself but batting shrinks 3%, the fabric will also shrink only 3%. Fabric shrinkage *is* a problem for quilts that are tied or quilted with lines far apart, as the batting will then not control the fabric.