I find basting spray much easier on my back and knees than pinning, and much faster.
My recommendation is to spray outdoors, if you can, to make sure you are not breathing in the spray. Someone posted about putting plywood on a couple of sawhorses in the garage to provide a raised surface with plenty of ventilation; I think that is a great idea!
If you do have to spray indoors, put down a large flat sheet to catch overspray; sheet can be tossed in the laundry afterwards.
I'm not sure about the spray not coming out in the wash problem. Maybe it depends on the brand of spray? I've never had to take a quilt sandwich apart after washing, so I can't be absolutely positive the spray washes out completely. It has just never been a problem for me and have never noticed it not washing out completely from a sheet used to catch overspray. Maybe it is harder to get out of batting?