I used to use a DCE Flickermagic ages ago with my A1200 and I think I can remember some of those nice copper gradients appearing colour banded.
I am now the (very, very lucky) owner of a CompServ Scandoubler II for my A4000 and AGA looks lovely now. :-)
It is a fantastic card - everything looks extremely crisp and sharp. The card itself is huge, it takes up the whole length of the video slot area and rests in the support railings. The S-Video and composite out are useful too.
I have still yet to figure out the best solution for switching between the SDII and my CVPPC; ideally looking for a nice monitor with dual inputs. :-?