Carl,
Fiji is a great diver's destination. I have never used a live-aboard, but can attest to the great diving off of Taveuni and Matangi. Matangi is my favorite because the "resort" is so pleasant. You can do boat dives and some of the best shore dives I have ever done. Lots and lots to see.
If you are interested in small things, Fiji has some of the most beautiful nudibranchs I have ever seen. Numerous dive sites will feature schooling barracudas and groupers that seem large enough to swallow a boat! On almost any dive you might see what I think is the most beautiful fish in the region, the Clown Triggerfish. If you are a photographer, they represent a real challange for selecting the correct strobe and camera settings: they just have such a large range of shades from snowiest of white to "coaliest" of black, and everything in between!
Oh, yes, do you like shrimp? Numerous varieties live in the Fijian waters. Perhaps the most novel are Popcorn Shrimp; they are like Anenomefish, living within the protective confines of stinging anenomies. And they look like little pieces of popped corn.
Definitely do Fiji if you get the chance!
Scorpionfish--lots of them there, too!