I recently had to make this same decision and settled on Fiji. I just cashed in 150,000 miles for two tix for my honeymoon in Sept. Now I'm not sure I'll be able to go. I just read that the resort that I have reservations at has closed for a few months due to low occupancy. I just hope the airline will re-deposit my miles if my trip is cancelled.
On a brighter note. All indications show that flights to-from the US have been operating as normal into Nadi. Also think of it this way, I was in Canada during the WTO riots in Seattle last fall. Canadian officials were discouraging travel to the US until the situation was under control. Sometimes I think the govt. warnings may be a bit over dramatic.
If you want to keep up on news about the Fiji Coup go to
www.fijilive.com or
http://businessnews.com.fj
Also here is the US State Dept. warning page
http://travel.state.gov/travel_warnings.html#f
Good luck.
-rollyo11