I like these thoughts. I'm gradually clarifying my own thoughts, and I think idleness is at the level of busyness, activity, etc.. that is, it just describes what you're doing at any given moment. As such, we all need some idleness just as we need some activity.
Laziness, on the other hand, has a moral component.. it describes the character of the person. I suspect some of these authors describe themselves as "lazy," when what they really mean is "willing to live in such a way that isn't merely busy." I'm fine if they use the term for rhetorical purposes, but it just doesn't reach me the way it seems to reach many of you. The reality is, nearly everyone in this forum is willing to make hard life choices toward a specific end, and that pretty much means nearly everyone in this forum is decidedly *not* lazy.
"Retirement," is a can of worms that isn't worth defining precisely.. we know what we mean here in these forums. :)
"Self-directed exploration," seems to be a great way to spend large swaths of time, and you only really have large swaths of time available to you if you're "retired." Same with "leisure," though that's a less precise term. Exploration could be considered leisure even if one is learning a ton while doing so.
Hopefully this was at least a little helpful. When living in the American context where busyness is often equated with self-worth, you often have to re-convince yourself over and over again, and I find having clear thoughts helps with that.
One thing I know for certain is that I've used up my scare-quotes ration for at least a fortnight.