Jake,
I understand your take on it. I have been crewing a lot recently and the spin on that boat can be pretty touchy (small curl turns into big REALLY quickly). Having the tales flying tells me I can stop letting it out/breathe rather than letting it out all the way to the point at which is curls a little- which quickly becomesa big one. I guess that is what I am looking for. Playing the spin really helps the speed downwind and having a little extra info helps. This is from a crew perspective downwind- the driver has the main and trav and all I am doing is driving the spin. Playing the spin alot sailing solo on the blade gets tiring but it is fast. You can really feel it pull when you let it breathe more.

Rereading your reply- if the tales are flowing are you going to get anymore out of the spin by then taking it to the point of having that curl? Or, going back to my original question- I guess with my spin the tales flying equals luff curl. Maybe some spins have more of a "sweet spot" than others.