You can get the ferry from Phi Phi to Lanta and then get a day trip to Ngai. Just explain you want to be dropped off there. When I did it they telephoned ahead and a longtail came and picked us up from the snorkelling boat. It might be possible to do that from Phi Phi as well though most of the daytrip boats I saw from Phi Phi around there were speedboats...private charters maybe.

Yes Ngai is changing (what island in Thailand isn't?). There are a few more resorts there now, upmarket ones of course. It's still very quiet though I think. I haven't been in the area for a year or two either.

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“Not all those who wander are lost.” Tolkien.
Life is not measured by the number of breaths we take, but by the moments that take our breath away.