I think its a good idea to give a student or transitioning pilot a go around without being able to retract flaps. A failure of some sort or a popped CB that won't reset will make that a scenario that is best to have some previous experience rather than being a first time for a low time pilot. Of course, a mechanical flap handle might preclude that exercise...
Regarding flaps and performance, we had a few 182's in one particular organization. One had flap gap seals, and the rest didn't. Doing a no flap approach with the flap gap seal equipped airplane and comparing it's much flatter glide ratio to the others was a productive exercise.