I've been keeping an eye one FS-UAE, as soon as they get OpenGL ES support it sould run at a pretty decent speed on the Raspberry Pi, certainly good enough for A500 emu.
Note: the Raspberry Pi only comes in two flavours... A 256Meg one and a 512Meg one... Both are overclockable, but the 512Meg memory chips seem more tolerant of the higher clock speeds. I run my 512Meg Pi at 1.1Ghz and my 256 Pi at 900Mhz
And the A9 boards I've been looking at already run SoftGL.
Not to mention that they run 600 MHz faster (with an already better processor core(s) - four of them to be exact), before overclocking.
And it has a more powerful four core GPU, four times the memory, and according to Pascal it should be able to run Aeros.
Starting at about $50 more than the Pi.
Also, I'm curious, how well can a Pi handle XBMC?