Hey Bog,
Sadly, I don't have the answer you want. If a hand had two fingers you could count the number of professional builders who built anywhere near minimum weight on one hand. Most amateur builds will be over by 10-20%. However, there's more to boatspeed that the weight of the craft. Look where the first woody came in the nationals last year - and that boat (by its owner's admission) was seriously overweight due to repairs if nothing else!
I get no favours with handicap but this will vary from club to club of course.
Re-sale value is one of the more salient points here. You are already in a more limited market with the boat being wood; add to that the fact that however well-built it is it is still a one-off and therefore not tried and tested. Sad really becuse, like so many dinghy designs, it was inteded to be built by the amateur. You could take a punt - I can guarrantee you'll have a really enjoyable sail but it really wants to be as cheeky an offer as you can get away with.
Good luck!