Haha what a great way to stir the bees! The answer is not "what should I do," its "are you willing to maintain a track throughout the day to accommodate both." Some tracks do it great, other tracks are running themselves into the ground. One thing is for certain, and that is bikes will show. Now quads on the other hand, they're a breed of there own. There's always couple vocal quad riders and parents that will fight to the death on this issue, but the truth is they don't support local practice tracks.
But hey its your track, try the 11-3 bikes and 3-Dark bikes and quads. Realistically who wants to ride the second half of the day on a hot weekend. So good luck with that idea.
In my opinion the best way to approach the issue on hand is to consult who is doing it right, Braircliff MX. Im sure if one were to go there and watch his operation one would see how/what is involved with making it achievable. I'm no track owner but i'd think there's little more to it then turning little dirt then adding some water!