I think what the OP is a beautiful example of is that there really is no downside to getting more training. And if the instructor is a good one and works to make the classes meaningful, there can be a big upside, even if you have a bit of experience under your belt. Most of us could be a bit better at navigation, or at maintaining awareness and buoyancy and position while trying to manage something like a recovery, and challenging yourself is the best way to grow.
Although I have issued with anyone paying the $30 fee for the PADI Master Diver card (since there is no additional classwork required -- once you have finished the class requirements, you just pay an additional fee for the "summary" card), I do not think it is wrong for people to take Con Ed. Just pick your instructor carefully, so you get the most for your money, as it sounds like the OP did.
Although I have issued with anyone paying the $30 fee for the PADI Master Diver card (since there is no additional classwork required -- once you have finished the class requirements, you just pay an additional fee for the "summary" card), I do not think it is wrong for people to take Con Ed. Just pick your instructor carefully, so you get the most for your money, as it sounds like the OP did.