After teaching a couple hundred students or so in the 6 pack classes... I found these to be interesting.
1. Only a small percentage of "boating their whole lives" had much actual professional knowledge. They had plenty of boat handling skills and possibly weather and sea sense...but technical stuff...not much. They were good enough to be safe boaters for general cruising...mostly.
When we moved to South Florida, I had documented sea time of over 2300 days and my wife had just under 1000 days. All our time was on an inland lake and in boats 30' and less. We had no professional knowledge. Handling the boat and docking and those things were second nature to us. Weather, sea sense, technical stuff, absolutely not. Safe boaters for lake boating, definitely. Safe boaters for coastal boating, perhaps in calm seas on a good day but I wouldn't say so. When we bought our first boats, we didn't take them out without captains.
Our first licenses were 25 Ton Inland. Took a while to get to 100 Ton Near Coastal and then almost immediately to 200 Ton. Slow to 500 Ton as it required days since first license. 500 Tons was nearly 5 years after first license.
Why? Lifelong learners? Pursuit of knowledge? Sheer enjoyment? We had decided boating was going to be a key part of our lives and we wanted to be as knowledgeable as possible. We're also not just nationally licensed but STCW endorsements (which adds considerable courses and costs). Have we gone overboard vs what we'd recommend for others? Definitely, but we enjoy learning. My wife's an educator and student and I've always looked to gain more knowledge in business so it's just natural for us. It's not for prize or title but just in valuing knowledge.
I'd suggest to anyone to think if there are things you'd like to learn more about in life in general. If they pertain to boating, look over the complete list of courses provided by schools like MPT. I do believe in regular coursework for professionals in any field. Some of the courses we've taken we have loved. For instance, anything with the simulators including Bridge Resource Management with Simulator Tasks, but rest assured that one isn't just fun and games pretending, it's challenging and stressful but I think could be of great value if ever faced with certain situations. It's one thing to recite Col Regs, but another to use them when you have to act quickly.
Some courses you hope to never need. I'd put Medical Person in Charge, Advanced Fire Fighting, and Survival craft and rescue boats in that group. After time in the fire lab, you're exhausted and ready to collapse. First sign of blood in our ER lab and I felt like I was going to pass out but then I imagined at sea and someone I was close to and knew I must push myself through.
My least favorite of everything is meteorology. Bores me to death, but important so I've done it. Marlinspike is nearly as low on my list but not quite. Also useful.
I believe if you're really planning on spending a lot of time on the water, then anything you can learn is useful. That includes classroom and hands on training. Do it not for a reward of some sort but just for the sense of accomplishment that comes with learning.
An example of learning after retirement just crossed my mind. What do you do after being President? You may speak or write, but George Bush pursued art. Most wouldn't call it great art although some of it has been well received. But you've held the highest position in the land and you keep learning something you enjoy.
I was saddened by a man I knew who worked until he was 79 and retired only when he physically had no choice. He never developed a single hobby in his life. He felt after retiring that he no longer served a purpose. I do recall his daughter crawling in his lap and saying "your purpose is being my daddy."
Pursue anything that you can be passionate about. One of those things for us is boating. Immerse yourself in your passions. Passion is what keeps you truly alive.