Some 14 years ago my family and I spent 6 weeks at Westin Denerau (then, I believe it was Sheraton) and used it as a "home" base. While we really enjoyed the staff, the golf and shopping in Nadi.
Our most memorable experiences were on other islands. Tavunni Is where you can stand on the international date line (I alone saw the real start of the new millennium on Jan. 1 1999, although as is the reality, it was a cloudy sunrise
).
Other memories were to the Yassawa Is. on a 5 day cruise with Captain Cook Lines that take you to the most incredible islands and snorkel/dive areas that Fiji has to offer (remember "Cast Away" with Tom Hanks, filmed up there
)
The real beauty of Fiji is not really the islands, it can be found in the true Fijians you encounter.