Bruce,
As to your first point/question -- why incarnate at all if one could duplicate any earthly experience in the afterlife -- I really don't know. Maybe it does feel more "real" to the experiencer if the experience actually occurs in a physical life on earth, or maybe it's just a matter of personal preference. Or maybe I'm wrong about being able to duplicate certain earthly experiences in the afterlife, I don't know.
Regarding your second point/question, if it is possible to duplicate any earthly experience in the afterlife, and if it would also be possible to choose not to know/remember during the experience that one was actually in the afterlife and not living through it on earth, then maybe no other souls would need to go along with the illusion -- maybe one could "live" through the experience entirely within one's own mind or soul. As I type this, I realize that that's kind of what I was thinking when I originally mentioned the possibility of recreating an experience in the afterlife. If that isn't possible, but if creating any experience in the afterlife is possible, then I still don't think the person would need for everyone with whom s/he had been in contact on earth to participate -- only those who were in contact with her/him during a particular experience.
That is, of course, assuming that the person wants to live/relive particular experiences, not her/his entire life. I don't know if the latter would be possible -- but then, I don't know if any of this would actually be possible. I'm just mentioning some of what I view as possibilities, but everything I'm saying here is my opinion only, as I have no first-hand knowledge of the afterlife (at least not any currently accessible to me).