Hiya Sally. Glad to see you figured out that you could keep posting all day and night if you wished. That shows you should be able to survive a trip to DV.
Accomodations are getting very tight right about now for December. You might try Beatty.
There is so much terrific hiking in the park, but I am not familiar with the mountain biking crowd. I must say I have never, read never, come across a biker on the trails. I have passed plenty on the roads.
Suggestions for hikes include the path north along the parking lot from Keane Wonder Mine and then up one of the several canyons. Dress warm this time of year as there is a big temp drop from the valley up the canyons.
Another favorite is the ridge walk that takes off south from the parking lot at Dante,s view.
But honestly, sometimes the best are to park your car off the road, and take off toward a direction that feels good. The park is a hikers heaven, especially a desert hikers heaven. Or go climb the dunes up north.
Carry much, meaning alot, of water. Happy trails.