I think that with things advancing much more slowly in the Amiga world, retro Amigas are more useful than the equivalent Mac. I have one of those machines, with OS8 and it's so slow it's unbearable, especially running 68k stuff, whereas my A1200/060/Voodoo3 feels an order of magnitude faster in everyday use. The Mac just feels so much more antiquated...
I recently picked up an iBook G4 1.33GHz for *nothing*. Granted, it wasn't working due to spilled coffee, but I cleaned it out and treated it to a new keyboard (€23 on eBay) and it's perfect now running Tiger. Not bad!!