I've also used the 505 to spray baste many quilts and have never had any problem with the machine getting "gunked up." I do always spray only the batting, though, never the fabric itself, because those instructions are on the can. I was really surprised to see Patsy doing that in her video, but it sure seems to work okay for her!
I don't have a big enough wall, so I do my spray basting on my craft table. I put the batting down, spray the part that's on the table, and then put the backing on. I just keep shifting the positions on the table until it's all smoothed out. Then I turn it over and spray the other side of the batting, and start smoothing the top.
I haven't had a pucker or wrinkle on the back of a quilt since I started using this method, and I've done the quilting with two different machines with no problem.