20 years ago, this would probably have been different. So we should perhaps add as an additional factor regarding value to the following features
size / rarity, workmanship, stones, and aura
also marketing and advertisement. Montblanc seems to do this well. From the current point of view the 146/149 look like iconic pens. Did they also 20 years ago? Who invented this type of shape and when? Is it a decendent of a Vacumatic?
I love the elegance of the pens from 1900. Long, slim, perhaps a beautiful floral decoration. But some really look like an awefull Chinese or Italian pen for which an pugilist could do an advertisement.