TN wrote on 04/26/12 at 13:14:18:
Studying these endgames are a bit like studying some middlegame positions - you may never get them on the board, but they teach you how the pieces function, which rubs off on everything else.
I think TN nicely rounds up the subject, especially his last comment, which I pasted again above. Frankly, this is the reason to learn such openings, even if you may never face them OTB. Pawnless endgames give you a nice feeling regarding coordination of pieces in the endgame - in the same way that learning IQP or gambit lines may do for you in the middlegame.
Regarding ELO considerations, almost none of my clubmates knows all of these, but that does not inhibit them from playing good chess. Myself, I studied these (except from B+B vs. N

) when I was about 1700-800 in strength. Practicing on ChessTempo like dfan mentioned has helped me a lot. I was good already in endgames so my results cannot reveal whether it has helped me or not. But I like to investigate some matters in depth even if sometimes they are not suited for my current level of strength. It's like a small investment in anticipation of me getting stronger someday

.
All in all, it has helped me in the same way as studying the Yugoslav Attack vs. Dragon. You learn sth new and improve as a player irrespective of its immediate practical value. Examining in depth sth completely new may have a positive impact on all of your current chess qualities.
P.S.: I mostly like R+B vs. R which has a lot of aesthetic value => Philidor was a genius!