Hi Callumstuart & All,
Anything other than 100% is a bit like "kissing your sister" -- sure it a girl but it's just ... not the same.
You only get the effects of totallity when it's total unfortunately. You'll be battling now to get any accomodation on Mangaia. There's only one or two hotels there and the total (regular) tourist accomodation amounts to about 20 beds I believe (and I'm subject to correction). It isn't a "resort" island. I was considering it but went to China last year instead.
They might have put some more accomodation on specially -- you should check I guess but all the die-hard eclipse chasers generally plan several years ahead and it books-up reasonably quickly.
Best of luck with it. The Powerhouse Museum in conjunction with Sydney Observatory are doing a tour to Easter Island to see the same eclipse:
http://www.sydneyobservatory.com.au/..._tour_2010.asp
pretty (very, actually) pricey though ...
... and I work there!!
Best,
Les D