Funny I should come across this. I haven't thought about flies mounted behind inline spinners in years and now have the subject come up three times in a week — this discussion, a comment a fly shop owner made and got a shadowbox of old flies for Xmas that had a McGinty mounted behind a spinner in it.
The shop owner, who ties a great many of his own flies for sale, said there was a lot of interest in fly/spinner combos just now but he was having trouble finding appropriate spinner blades.
The shop is in Richmond Va. and I suspect the interest in fly/spinners reflects the smallmouth orientation of that area. I also suspect it reflects a lingering lack of confidence in their and their equipment's ability on the part of newer flyfishers. I can recall figuring ways to use my fly rod as an inefficient spinning rod before I learned how to actually catch fish with true flies.