Hehe... I never said I was an expert or pro at anything but I just got tired of disclaiming that fact in every post. Maybe I should add that to my sig.
I'm not saying either way is better just yet but I'm pretty sure the run dry method evolved from people who got used to doing that via batch sparging. I think this is a good question to poll folks about.
Why the switch to fly sparging? No reason other than to try it. I caught a good deal on a better pump and thought having two at my disposal was a good enough excuse. I hope I never leave well enough alone.
My brewing experience is paltry compared with yours, Bobby. However, I don't think 71% efficiency constitutes sucking. If you consistently hit 71% I'd say you have a pretty solid process. If you're in a constant flux between 71 and 91, that would be sucking.
I drop the sparge water right onto the top of the bed with a piece of silicone tubing. No sprinklers or anything.