The Mediator is also handy for big box Amigas. When I installed a Mediator in my A4000 I ordered a 256MB Radeon card from Elbox. While I was waiting I tried two ancient and dusty ViRGE cards I had lying around that were salvaged from old PCs and they both worked brilliantly and certainly felt as fast, if not faster than my Cybervision643D. Another "junk" SB128 card also worked. If you just add up what a good Zorro graphics & sound card would cost you then that certainly helps to offset the cost of a Mediator board. Of course it would be nice if the software for the Spider card was available/worked.
I have a towerized a4000 with Mediator 4000D. Now that I have finally gotten all of my pci cards working (voodoo3, spider II, fast ethernet, sb128) I have a fully expanded and very versatile computer

Granted, I have a cv64/3d with scandoubler for everything the voodoo3 can't do...basically, most things aside from workbench, actually, but at least my wb looks great. The USB and fast ethernet are AWESOME. I guess now all I need is a ppc board

But yeah, I'm a believer in the mediator. It makes the A4000 quite a bit more interesting, without taking anything away.