This is not the project boat I may have seen. This is really bleak, Paul. Here's my opinion: First off, the boat has been neglected for so long, it has no value. In fact, unless someone takes it off the owners hands to restore it, it may be a liability if he(present owner) has to dispose of it(sad to think). Unlike neglected wooden boats that ultimately turn to compost, these hull and decks will be around for ions and won't just go away.
It is restorable but it's basically just a hull now. On the bright side, as the Challengers are solid glass-hull and deck, that makes restoration-no matter how involved- possible.
I think the cabin looks beyond clear wood restoration. The cabin may be sound enough to repair and ultimately paint, which is not a bad treatment at all(we've seen a few Challengers nicely finished that way).
As I am contemplating building my entire cockpit in a shop, and installing it as a single component, I don't see this rotted cockpit that daunting. But taken as a whole, this is an enormous project.
Going to your other question, what would it be worth if fully restored? I'm afraid, like many boats today, a restored Challenger isn't worth enough to cover the investment(not even close if you hire much of it out). That's not the designs fault, it's just the market is not great.
I wish I had more good news!
I'm for restoring them at any state but I have to be honest. I'm hoping someone else will chime in. There's is a lot to talk about with the photos you posted. I think they show the achilles heel of the Challenger. If neglected(as this one has been-severely in fact), because of the unique wooden aspect of the Challenger design, they degrade very rapidly.
Have you looked at any other project Challengers or ?