RE: Wind indicators
I should emphasize that I don't have a yachting/dinghy background, but I think I might be able to offer a reasonable perspective with respect to windsurfing. I think that AlexWind is right on track here about the "feel" needed in windsurfing, because I think that windsurfing requires an intuitive sense about wind, water conditions, the desired direction and especially the sailor's response to everything at hand (and through the feet). It must be remembered that speeds can be far greater, and that a windsurfer isn't sitting down in a position that allows one the easy opportunity to assess how telltales would influence performance. Really, a windsurfer must concentrate on what's happening ahead to best formulate the best strategy. That definitely doesn't rule out the advantages of deciphering the best racing techniques under the circumstances, but again, I think that performance requirements must be more intuitive in nature.
In reality, given the number of years windsurfing has been around, and particularly thinking about the fact that competitors always leverage off of obvious advantages, why doesn't anybody use telltales in windsurfing compeitions? No doubt, this says a lot about things, at minimum, concerning the value of telltales in windsurfing.