I wonder if the idea of what's a 'classic' is mainly a generational thing. There are some solid gold classics, because they were ground breaking and special even when new, Brough Superiors, Vincent Black Shadows and the like but they were hand built in limited numbers and will always be valuable. Even bikes like the early bonnevilles and 500 Goldstars that are now fetching £12-15,000+ were churned out by the 1000s and are still relatively plentiful and even humble commuter 350cc Matchless and AJSs are going for £2000+ but who's going to be buying these bikes once the guys who used to ride them in their youth have all fallen off their perches? I love the old British bikes but I wouldn't want to own one. So when the number of people wanting these bikes is fewer than those available, the value is surely going to drop and some owners will get burned. I wonder how many 17 year olds just getting into bikes now are looking at the old Z900s and CB750s as the bikes the want when they can afford them, I suspect not many.