I'm sure taking the DM course is one way to help make you a better diver--and it's no doubt the most widely publicized way--but we shouldn't forget there are other ways.
Hi Don't disagree with you one bit. I used the examples I did because this was a thread asking about the value of the DM course. Also because what you wrote was exactly my thoughts about the DM course before I took it
If I can pick up on one part of your post.
Why spend time on learning to lead dives and teach others when you could spend that time on learning what is really your goal?
So I entered with pretty good skills, certainly more than adequate for Rec diving. However I soon found that being in very shallow water magnified deficiencies I had which weren't apparent in normal diving. I mean who spends their time in only 6' of water?
Having refined my buoyancy and positional finning while being task loaded - i.e. focused on a student rather than what I was doing translated into much better Rec skills. Had I not taken the course I wouldn't have a) had the chance to fine tune those skills b) Even known that my skills could be fine tuned to that extent.
I often encourage people to take Tech 40 (in the PADI world) Not so they can become tech divers, but because the skills and knowledge can easily improve someone's Rec diving experience - even on a 30' bimble around a reef.
One thing that was reinforced to me post DM course - was that you never know with any course what nuggets of information or experience you might learn. It's often not apparent from the course outline.
While taking courses or working with a mentor on subject you want to know more about or know you require extra practise with is absolutely a good thing. As I found it's the unexpected things you learn or skills you enhance unexpectedly - often those you think you have down pat, which are the greatest learning experience.
So while I would never say the DM course is the end all of all courses, I maintain that with a good instructor and an open mind, its surprising what you learn and how that translates into your normal fun diving, and can be a worth while course without wanting to guide groups or teach students