We always buy trip insurance. We book through AAA and their prices are quite good. One summer with a delayed trip due to a baaad case of poison ivy was all I needed to never be without trip insurance.
One sure rule - If you buy trip insurance, you won't need it!
I never have in the past, but this is a pretty big trip and the cost was very reasonable so I opted to get it. Hopefully we won't need it but if we do we are all set.
Count me as another who never bothered with insurance before, but for our upcoming family "trip of a lifetime" 8-night AKL Platinum package trip it seemed really silly not to (premium was just a little over $100 - the package cost us over $10k)