Hi Again!
Green Class in Kyushu is really nice! When I first came to Japan I was soooo impressed by the Shinkansen and thought that normal class already was 1st class compared to trains elsewhere in the world (looking at the UK in particular). Than last March I had the change to explore Japan on a 3 week Green Pass and now I don't want to go back to normal. Normal class already is amazing the first time that you come to Japan but Green really puts the cherry on the top!
I really think that a Green Class Pass is money well spend but you have to be in the position to spend it. That's why I would recommend a normal pass to most people however.
PS if by Kurosawa you mean Kurokawa than you can use the JR to travel to either Aso or Kumamoto and take to bus from there to save some money (it's also a good excuse to get an Eki-Bento).