I think whichever side you take the important thing is to be consistant.. if you pre-wash, wash everything.. if you think it's just fine the way it is, then keep everything that way.. At least then you know for sure and won't have a quilt with mixed fabrics.
I always pre-wash.
Besides not having to worry about shrinking problems and bleeding, it allows the fabric to relax and return to it's natural state.. being machine wound onto a bolt distorts it and makes it hard to cut on grain. That's why when you go to straighten it, it is sometimes way off. It's been wound on the bolt and the inside turn of the fabric is shorter than the outside.. It doesn't roll on there straight and it's crocked when they roll it off to measure it. It stays that way (unless you happen to get your piece cut at a time when it's still pretty straight)unless you pre-wash it.
I usually don't pre-wash kits or something like a jelly roll.. That could be a mess.. and those things are not put into the general population of my stash.