If that is how OSP is looked on, that is a big shame. For me, it always proved to be a learning ground. You are wrong in "doesn't teach anybody anything" part, totally. That is exactly what teaches anyone anything. You spend several hours trying to figure out the problems and learn several things along the way.
Measurement of a project's quality is parallel to hour spent on it, aka the effort put into it. The details, care and the will on how the message is delivered.
I wish, Diplomacy mod had never gone OSP eliminating all the need of a better one, where diplomacy lacks and giving the modders the confidence better cannot be done. If you are content with it, well...pretty much a bad attitude for someone in your place.
Answer me in something. What do you mod for? Spend all that time for Sayazn, which is coming up pretty nicely but also unbalanced, uncompleted and sketchy in several aspects. I used to mod for innovation and because I loved it, not for the community. (Not that I don't care about them.) To me, giving diplomacy a credit for the inspiration of my own "Diplomacy" mod sounds a lot more satisfactory than boldly giving it away. Not knowing what a single line in the system does.
You tell me. What is the benefit of using OSPs if not to get inspired and learn? Illusion of depth and hardship probably.