I really enjoyed my course. It was interesting and engaging and informative, and I did get some hints and tips, about changing gear and so on. (Hah, wish I could do that in my car just now - it's about to be very expensive after the gears went entirely last night...) It was also interesting hearing perspectives from bikers and lorry drivers, because I don't have experience of driving those myself.
We had a mix of people on our course - including a couple of new drivers, whose parents had paid for them to take part as part of some pass plus course or something, rather than them having yet been caught speeding. But I'd say there was no particular age group in the majority.
Once you pass your driving test in this country, you don't have to do any sort of refresher. But the rules of the road may have changed since we passed our tests, and I'd put money on it that most people don't regularly check the Highway Code just in case. I also think that people who have been driving a number of years will have probably picked up some bad habits along the way, which they may not be fully aware of - particularly if they do a lot of driving - when my gears went last night, it made me aware that I'm not usually very conscious of changing gear, because I'm doing it because of the sound and feel of the car, I don't need to look at the gear stick at all, and it all just works without me having to think (until it doesn't) - it's a good thing when skills have developed to that sort of unconsciousness, but bad habits also develop that way, not just the good ones.
IMO, it's the people who say they don't need to go on the course, and are arrogant about how well they drive are the ones who need it. There is not a single driver among us who couldn't do something better, not one of us who won't have been involved in a near miss, whether through our own fault or not, and some of us will have been involved in crashes, too. Each one of us could have made different decisions at the time which could have made the outcome better or worse. I think the majority of us get it more or less right more or less all the time, but the course is there to help with the times we might not.
I would happily do the course again, although I don't plan on being in a position to do so (apparently you can sign up just for interest, though - no idea if this would count against the "one course in three years" thing if you then got caught speeding within this time; the aim of course being that you wouldn't be speeding to get caught anyway.)