All good thoughts. Now, let me make a few specific suggestions. There are a number of factors going to the category "classic." For bikes designed for performance, how they performed is a potential indicator. Innovative design could be another. For example, the Litespeed Ultimate saw a good deal of international competition during the 1999-2002 period, as well as podium time.
Another factor is classic design, similar to the predecessor steel road bikes.
Very nice bikes.
Those sure are some odd looking dogs, though.