I've also considered spending a week riding in the Death Valley area during March, when most of the flowers bloom. Like you, I've been there by vehicle a couple of times. My biggest concern is where to legally camp. There are some very long distances between campgrounds, and even in March, it can be quite warm, so water supply is also important. Regardless of which routes you choose, it's an exhausting climb each time you ride out of the valley as well.