Rolf,
I attempted to attach a photo of the carbon boat some people asked what it looked like.
Your question about how would the efforts of a dedicated amateur builder stack up against the stock boat is a good one. Deserves a detailed answer. First some thoughts about how the boat structure has progressed through the years. The original plywood boats had marginal durability by standards in those days. But as materials and process improved the margin that was gained was invested in extra strength and lifespan; not reduced weight. We are at a point today where the boats far exceed the normal standards for production catamarans. This is not a bad thing if you are a serious competitor; you want the boat to perform every time with total reliability. One thing though that causes me doubts is having only one builder for the class. I own a stock boat too and the quality is superb but... The composites industry has been going through changes; material prices have gone down a little, processing is becoming easier, new methods reduce cost (e.g. resin transfer molding). Do you expect to reap any of these rewards from the builder? You should. The concern is that a business with a monopoly sometimes does not have the incentive to compete in the market.
In an earlier post some one asked about wood boats. I certainly agree with the opinion wood boats can no longer compete. For one thing, the rig loads are significantly higher the way the boats are sailed today. If someone wanted a boat for recreational purposes (NON RACING!) they could build a plywood boat and replace the original e-glass hull lining with more modern fibers. Plywood hulls are cheap and relatively fast to build. A perfectly good recreational boat would result; not class legal and not for class racing.
Now. On to the real question. As you go up the ladder of better and better composites performance, the majority of time and money is spent getting the last possible small gains in strength and stiffness the material has to offer. The difference between prepreg cure with a vacuum bag and that cured with an autoclave is actually quite small. I would not recommend to any one at home to attempt making tooling for elevated pressure cures. It's just too hard; I know as I have attempted it. The best practical technology is the vacuum bag with a heated mold. This gives you the option of using either wet lay up or prepreg along with your Nomex core. This type of mold is quite practical to make but becomes a lot more attractive is the effort is amortized among 3 of 4 boats instead of a single one.
Prepreg has three advantages over wet lay-up:
1. Almost unlimited open time in the mold to assemble all the parts and get the bag hooked up and sucking.
2. Lower resin content resulting in slightly better physical properties. Resin content usually 38% for prepreg vs. 48% for wet lay-up.
3. Totally uniform and reliable fiber wet out with the prepreg.

The prepreg advantages are not really that great in real life. To bond to honeycomb fabricators add a layer of film adhesive under prepreg that brings the weight up to close to the 48% resin content of the wet lay up. Some of the new wet resins allow up to 12 hours of open time so that's not such a big deal anymore. Attention to detail from the craftsman can go a long ways toward ensuring uniform wet out.
One of the biggest problems for doing this kind of work is obtaining the materials at a reasonable cost. Fiber distributors only want to deal with people who work "in the industry". If you tell them you are building a boat in your garage they will give you a look like you smell bad or something. My way around this is to make up a ficticous company name so they will sell to me. This is not unethical since they really want to sell material but just need some help overcoming their prejudice. On account applications they have a space to fill in asking your position in the company. Sometimes I call myself "engineer" or "materials purchasing": depends on my mood that day. One time I promoted myself to "Production Manager" and became an executive in the company! Anyway, I now have lots of good relationships with suppliers.
The CLASS LEGAL boat you would end up with would be significantly better than the last generation of Tornados built with foam cores and vinelaster resin. Strength and stiffness pretty much the same as the current production boat. I would give the production boat a slight edge on durability but not enough to kill the idea. If there is a slight loss of durability, that would have to be traded off against cost.