I'd second that. I've stayed at more or less expensive ryokan (though admittedly never in the price range of Gora Kadan), and my most memorable onsen experiences have tended to be at more affordable properties pretty far afield. In general, places in remote areas that still manage to score high marks and many votes on sites like Jalan or JTB seem to be pretty reliably good.

For example, I have fond memories of a stay at Shisen in Aizu (Yunokami onsen), which is a modest family-run minshuku, but still offers large, comfy rooms, nice jizake and local mountain cuisine, a kakenagashi rotenburo, and really warm service (the wakaokami would tell you everything you wanted to hear about the calligraphies on the wall, the story of the place and so on). The area is fantastic in the season of automn leaves.

Goshoranba near Izumo (Tachikue-kyo onsen) was also a great experience (incredible views from the rooms and the baths, surprising hiking trails at the doorstep, a very filling dinner, etc.) all for the price of a business hotel.

Clearly, though, neither of those is like the traditional Japanese version of a Four Seasons night. For that, and the feeling of splurging at bubble-era rates, Gora Kadan might be a good choice.