Nick,
The Mozzie is a great way to introduce yourself to F16 or spi. cat sailing in general, so stick with it for a while. There are a lot of sailors who desperately want the Mozzie to stay a 1966 design, can`t fault them since it worked well for Hobie. The Mozzie unfortunately lacks the big corporate marketing machine that is Hobie, and I believe that it will need to take the leap forward at some time, or be remembered as a nice little boat that you could sail if you couldn`t afford a Taipan. I don`t believe changing sailplans etc will make it as fast as a Taipan, but by narrowing the gap you will make it that much less attractive to sell the boat and get a Taipan, so I believe constant gradual development can only do the class good.
Darryn sails uni-rig from my understanding based on previous discussions with him, and from reports I`ve heard from him he tends to beat the sloop-rigged Taipans when the wind is over 20knots. Now call me confused, but in S. Africa the sloop Mozzies are faster than solo in over 14knots, in Aus it seems opposite. Too many variables, could be the solo sailors are the better of the bunch ? Another variable could be that the Taipan sailors Darryn races are not the top of the fleet, but only Darryn can answer that. Yes, I`ll agree with him that learning the boat and working at it will narrow the gap, but as Wouter says, problem is when the Taipan sailors do the same.
Remember, handicap ratings are imperfect, the Mozzie may be easier to sail than the Taipan in stronger winds, making it the "faster" boat in certain conditions. If you don`t already have the spinnaker, get one, it will make racing non-spi Taipans very interesting !
Oh yes, and send pics of your mainsail rigged on the boat when you get your mast sorted.

Steve