I think that their resale values will remain higher than their PC counterparts, but I don't think that today's Macs will be as interesting to collect as Macs from the past.
Older Macs, especially from the PPC days, were very unique to other computers and electronics.
The iMac G4 for example, is my favorite Mac design. It is beautiful, unique, and really stands out.
Walk around a Best Buy today, many of the laptop and all in one computer demos look very similar to Macs.