eh? Are you mad?
With the software base of the Mac, a cube is 1,000 x more useful than any Amiga (or clone).
As well as upgraded GFX/mem....there are a whole raft of CPU expansions for it if you feel like investing the price of a Pegasos you can get 1.5GHz G4 ;-)
Personally I got Powerlogix 1GHz G4, NVidia GF3, 1.5GB RAM and a DVD-RAM/RW / CD-R/RW MCE superdrive in mine and running OSX.3.7.
That said, you could eBay it to some foo' and put the money towards a G5 machine ;-)