Interesting thread. My personal "goals" for road riding are speed and endurance. I like riding timed century events with plenty of climbing. I simply like the challenge and riding with like-minded people. But when I go mountain biking I chill out much more and enjoy the tranquility and interesting terrain. No timing, no power meters, just riding the forest singletrack. It's a whole different mentality. I find riding slow on the road a bit boring if I'm honest. That's not to say I don't enjoy a slow recovery ride, but I wouldn't want to be doing that all of the time. So I expect I will migrate more toward mellow off-road riding as I get older and slower on the road.