Half a year ago; I would have said yes. Now I wouldn't be too sure.
There are upsides and downsides. Voodoo3 on Mediator is faster then even a Picasso IV. Cards are cheaper to buy.
But then again, you already have a NIC and a (decent!) GFX card. That means you invest a lot of money on "just" a cheap audio card if you want one. If the money needed justifies the speed increase; that's only for you to decide.
If you do go the Mediator route give me a buzz if you need a soundblaster card; I got a loaded box of new OEM SB128's from a local computer store

EDIT: And yes, you can still use your Kickflash. Even your CV64 and X-Surf if you want...