Hi.......yes, it's a very good deal to get free gratuities and $300 onboard credit. The tip for bars/waiters is covered in the price of the drink.
Suggestions on saving money:
Avoid the spa, it's run by Steiners which means prices are outrageous and the quality sub-par. Other than that, keep alcohol to a minimum and don't buy anything on the ship.
You can use the $300 credit for shore excursions. I don't take cruise line shore excursions, I do my own for a fraction of the price.
Crystal is wonderful, the service one of the best in the cruise industry. It will be a fabulous cruise!