Chuck,
The value of used or collectable bows is determined by the market--what people are willing to pay, or not pay, for them. These bows may not be for everyone, but many enjoy owning and shooting older equipment. One person's opinion that the bows are only worth so much is just that, opinion. Also, many of the older bows perform as well or better than some of the 'custom' bows, despite the difference in price tag.
As far as bows 'letting go'. It could happen with any bow, new or 30 years old. Generally a bow bought used will not have a warranty anyway so age is a mute point. The big difference is that you paid a lot more for the used custom than you did the used Bear. As far as bow failure, I have never had an old bow to break, I have had 3 customs however that did.
As far as 'bad apples', I agree the moderators do a good job keeping things in order, just as the auction site does too. Personally, I have never had a bad transaction at either site, however I do ask questions and only buy something if I feel comfortable with the seller and their information. Common sense really.
Where can I find a good used bow for $100??