I think it would bring about $400 to $450. The Bisley stuff on it will help, and so will the pretty white grips, but I don't think these guns are in really high demand, especially since Ruger has brought out the Bisley New Vaquero. I know--yours is a heavy frame Vaquero, but for those wanting to shoot high pressure loads there are plenty of Bisley Blackhawks available for around $400.
As nice as the Vaqueros are, their value is kept down because they're just so numerous. Take, for example, the BRAND NEW birdshead Vaqueros that ACRYLICTNK has right now for $499 shipped. Another example: I recently bought a stainless Vaquero in excellent condition with simulated ivory grips for $500--with a holster and belt, about a hundred rounds of factory ammo, and a few hundred empty cases.
What you have is a real nice gun, but not one that will fetch a premium price.