The following are my 2 cents. In short, you have plenty of issues need to work on.
1. DEN is a UA hub. So it is always better to fly SFO-DEN in hope for better award inventory.
2. You can also fly WN with SFO/OAK-DEN.
3. Except emergency, it is pretty much a waste to spend 50K in for a domestic economy award ticket.
4. Detail about your proposed travel is needed.