Two additional factors to consider are hostile legislation and technology advances.

The first is obvious, especially if you live in the EU.

The second is not so obivious. Advances in 3D scanning, integrated with CAD-CAM technology make the duplication of old masterpieces a realistic possibility. Not in the sense of forging by crooks but of recreating the exact same item faithful in every detail, and with more sound modern materials. Such capability is bound to have an effect on the price of the originals, positive or negative is hard to say.