Now I have some time
I use a few Emulators on my Amiga's such as ShapeShifter (Mac 68k) ZXAM Spectrum, ASP (spectrum) CoolNES, AmiGameboy, AmiMasterGear and Mame060.
I've tried others with varying success but I find the above work really well.
On your 020 @ 25mhz you will be able to Run most of these just fine, Mac you might want to stick to Mono stuff and CoolNES might be a touch on the slow side.
For Spectrum on your setup ZXAM will be smoother/faster but ASP is more accurate, I particularly enjoy using ASP on my A4000 as it supports AHI and RTG so I can use my Graphics and Sound cards
The Console Emulators benefit from a CD32 controller to give you access to all the buttons.
Mame is only for 060's and really needs RTG to be playable so not much use to you! Even then you can only really play basic Games like Pac Man, Donkey Kong, etc.