Is it warm there in March? CPh-Flyer could probably answer your question better than I as I’ve never been to Ishigaki but I was pretty unimpressed with Miyako. Don’t get me wrong, the water can be beautiful, but the hotels, beaches and restaurants weren’t as nice as I would have hoped. It all depends on your expectations I suppose. If you don’t mind a lot of run down ill maintained infrastructure and really are going for the water scenery, then you may enjoy it. Further, it wasn’t super pricey compared to say, Hawaii or Tahiti. Depends on what you want as usual in life