Hi Darryl,
I think there`s always the temptation to upgrade to stay cometitive with newer designs, there are 2 schools of thought here : Stay One-design, don`t change a thing, ie Hobie 16, Dart 18 etc, or go development class ie A-class, Tornado, Mosquito & others. The first group are successful because there`s no continuous development costs to stay with the pack, you can buy a 1979 Dart 18, go to the Worlds and still be a top 10 finisher (Johnny McGillivray did just that at the `99 Dart Worlds, but then he`s a Hobie sailor ). Hobie have their own style, and enough cash to back it, and that works too. I think these classes are losing some support to more exciting, faster classes & this will only increase as more high-tech, lightweight & exciting boats are introduced to the market. Of course, these newer boats will have to get their marketing right, or they won`t succeed.
On to development classes : To stay competitive in most classes you need to buy new sails every 5 years (or even less in the case of Dacron). By looking into upgrading the design of the sails every so often, a long-lived class (ie Mozzie in this case) can extend it`s lifespan in the market, but there are limitations, with regard to what the platform can support in terms of rig design,as well as what is financially feasible to the boat-owner. That`s why 16ft-ers are becoming more full in hull shape, not because i`ts a better low-drag design hull, but because the designers are putting 18ft rigs on 16ft boats. The Mozzie hull shape is so similar to Tornado, which is regarded as one of the best hull designs (by some, not all will agree), but because it`s a scaled-down T, it has less hull volume than the newer 16ft cats, so it won`t hold the same kind of rig power well, except in light airs. This, I believe, has been tested by Bob Wilson in the Mozzie class in Aus with limited success, and is evidence that a taller rig with more sail area doesn`t improve the boats heavy-air performance much. A few years ago some Auzzies put a squaretop sail on the existing mast length, with no apparent increase in performance, which killed that initiative. An interesting thing is that if you took a Tornado & scaled it down to 16ft, it would look like a Mozzie, but be 22cm wider and have 20% LESS sail area than the current Moz design.
The problem with changing the rig design is that not everyone does it at the same time, not everyone can afford it, and you lose some sailors along the way. It took us 18 months to get the spinnaker into general use by 80% of the fleet, for the first year there were only 6 of us. Four years after the lightweight hulls were first built here, and we still have older boats that are now not competitive, we accommodate them by having separate classes, but these sailors are saving cash to change up to newer boats. If we were to spring a new rig design on them now they would just pack it in and go buy a Hobie, or quit sailing. Development classes are a good thing, provided that development occurs within strict one-design rules.

There, I`ve had my say, and it took a while.

Have a look at how the Mozzie is developing in SA on our web-site :
http://mysite.mweb.co.za/residents/tuffex/boat_report.htm