I took a Craftsy class today--"Design It, Quilt It: Free-Form Techniques" taught by Cindy Needham. She's a big proponent of stitching in the ditch--she calls it ESS (if I remember correctly), Every Stinking Seam. She says that doing this anchors the blocks and stops your fabric from creeping across BUT here's the catch, she pin bastes her quilts. I don't think that you will have the creep factor if you are are spray basting. A walking foot is good if you are doing straight line stitching because it moves the top layer in tandem with the bottom layer (I don't use a walking foot when I've spray basted because my fabric doesn't move) and I think a ditch foot won't be necessary if you're careful as others have said. If I had to make a choice, I'd get the walking foot. Cindy showed samples of quilts made with and without stitching in the ditch and I have to admit ditching did make the quilt look a little better. Also ditching before you add your other quilting adds a lot of extra time to finishing your quilt--depends on how fast you need to get it done. That being said, as long as you use enough quilting throughout your quilt it won't fall apart.