It depends. I do buy fat quarter grab bags on Whittle's Fabrics' site - the shirtings, the cheddar and poison.
If the grab bag was themed appropriately, yes "I Spy" or "Canning Jars" or "Plaids/Homespuns" or "Civil War" or "1930's" or "Purple/green florals" or "Autumn Leaves" or something like that, then yes, I would buy them. Or if it's a mixed bag of Thimbleberries or Kansas Troubles lines or Robyn Pandolph lines or Debbie Mumm or Mary Engelbreit.