Hi! Port Vila is great for duty free shopping. Fung Kuei Duty Free was a great place to shop.
Blue Lagoon is an amazing place to visit, as is the Cascade Waterfalls.
Last time we went to Noumea, there wasn't much to do, but we were there on a Monday in the afternoon and everything was closed.
Don't know much about the other ports. I'll be doing some research on the must see and do in these other ports.