Hi Darryn,
You are fortunate that the class is big enough to do that - we are only 20 odd boats, so a decision had to be made to either adopt the spinnaker, or drop it altogether. There were 5 of us with kites that basically lapped the rest of the fleet at club races (didn`t use them at nationals the first year, obviously).
We were actually very surprised when put to the vote, 100% of the fleet voted for the spinnaker, even though only 20% of us had one.
I think the reasoning for it was that we are competing with other classes for attention with respect to getting new people into our fleet, and making the Mozzie a more attractive option than a H16 or Dart 18 (predominant fleets here), as well as a far more cost-effective option than a Hobie Tiger, but still having the spinnaker for those that want a spi boat.
Of course, "more attractive" can have it`s down-side too, as it`s probably a bit overwhelming for any new sailors or non-sailors to feel confident enough to sail the boat. But then you can`t have it both ways (Well it seems you can, in Australia )

We did look into the option of squaretop sails, but without lengthening the mast it really would give little benefit. I don`t believe the current mast section would take much more length, so a different section would be necessary, and costly. You guys are quite fortunate, if you wanted to experiment with this you could pick up a used Taipan mast and start with that, but then the hull bouyancy could be a problem.
It`s a perfect little boat, lets keep it that way. (With spinnaker )
Steve