The whole ryokan experience is meant to be spiritual and sensual. It is structured to awaken the senses, though in a Japanese way instead of a western way. If you are tuned in to that, it becomes very erotic; the best sex of my life was in a ryokan. Your body merges with the universe; somehow the ryokans really seem to accomplish that. But YMMV, so don't let that colour your decision on whether it is worth the price (btw your ryokan is moderately priced, easy to spend triple that in Japan). In my mind the question isn't whether one night is enough, but are 2 nights enough?