Anyone spent time on Naoshima the art island?

I have been told the idland is womdefful and a few days are needed at leasset. We are spending 15 days in Japan in the Spring and would like to get opinions.

My last trip was three days, and the first one around three hours. Depending on what you want to see and do, both work.

Go to the Benesse house website and look under suggested itineraries (they may call them "courses").
You'll see sample day, 2 day, and IIRC 24hr itineraries.
I'm not saying you need to follow any of them, but they'll give you a decent idea of how long it takes to do things.
Ive been there 4 times, and my ideal short stay is to get the early boat on day 1, do all the art sites and museums except Benesse on that day, do Benesse on the morning of day 2, and then leave.

I spent about 24 hours there, and felt it was enough (although I'm sure there was more to do). Had time to see three or four museums (they're small), all the Art Houses, and do a lot of walking around. I stayed at the Tsutsujiso yurts, which were nice and very inexpensive.