I think you 18 owners are missing the point. Noone (as I read it) was dissing your ride - I think that many of the catsailors on here will have only very fond memories of 18s - the question was is it worth spending more money on the boat?
What does an 18 fetch in the USA? In the UK/EU they seem to run around the equivalent of $1000-$2500. With new hulls will you ever get ANY of that extra money back?
There are surely other options -
1) buy the very best used 18 you can find
2) have the existing hulls professionally refurbed
3) hunt out all those unused/unloved 18s around and cannibalise them to build up the best boats you can as well as a stock of spares.

Some of the 'vintage' dinghy classes in the UK (FD, Hornet, Fireball) have done just that and now have a thriving racing circuit once again. This has the benefit of raising values for existing boats and some people even considering building new boats!
Whatever you guys decide to do - enjoy your sailing.