Rare? I would say good shape, non-yellowing working Amigas are getting rare. Of course, the majority of people under 30 don't ever remember Amigas - I even have co workers who never heard of C64 - much less Amigas! I have bought 2 working A500 recently on ebay from people who didn't really know what they where - they where cleaning out closets/garages of family members and ebayed them!
The other issue is why would anyone want one? I wanted an Amiga cause I had one when I was in elementary/high school and always wanted another after mine died. But besides someone who had one or a computer history buff, the desirability is slipping.
Amiga Computers where always niche and never mainstream compared to crappy PC clones. Even the Apple machines of the time period didn't sell well - and Apple almost went under too!
Amiga's are great fun for me and anything related to them is desirable to me... but unless the cost of the PPC Amigas come down, even the hobbyist market will go away as they degrade....
But on the bright side, apps like WinUAE will be here a long time to come so I can show my grand kids the first real OS I ever used!
My 2 cents worth....