I would rather not burn my 2 points on a mule deer tag if it is going to be wasted.....I am going there to hunt elk.
You may have just answered your own question.
Also, have you considered if you want to deal with two animals on one hunt? That's a lot of work, and a lot of meat to deal with.
Finally, think about how you'd feel if you had a chance to shoot a nice mule deer, but didn't have a tag, and you didn't shoot an elk. Would you then be sorry you didn't buy the mule deer tag?