Spend the time watching the beautiful scenery and listening to live music instead of driving to the grand canyon. The service attendant shared information about the historic train cars and the desert around us as we traveled. First class was worth it with more comfortabe seats (all facing forward) and snacks. We got a package deal with a two night stay at the beautiful Grand Canyon Railway Hotel which we thought was fairly priced. In any case, we don't mind paying to keep this piece of history running. The "train robbery" was a little hokey for grownups, but it was fun for the kids on board.
At the Grand Canyon we took the shuttle to the most highly recommended look-out points and still had enough time left to do some hiking. That was without wasting time on a sit-down lunch, though. A very enjoyable day!
PS, if you have a national park pass (annual or senior) GCR will deduct the park entrance fee from the price of the train ticket. Enter the pass number online when you buy the ticket and bring the pass with you when you pick up the ticket at the station in Williams.