The Mountain Room at Yosemite Lodge is a nice, less expensive alternative to the Ahwahnee for a relaxing, good meal. Not to say it's cheap; you’ll still spend $50 to $60 for two people, but it's less expensive, easier to get reservations, and if you're staying at the Lodge, more convenient.
The Mountain Room is more kid-friendly, so don't expect as quiet or romantic of a dining experience. Request if possible a table near a window - it'll be quieter, plus, depending on the moon phase, you may get a lovely view of the Falls. A series of gorgeous color photos of Yosemite are hung along all the walls without windows.
The food is tasty continental/California cuisine, steaks, fish, pasta, chicken, etc. A nice wine list is available. Desserts are good. Fresh loaves of sourdough bread are brought before the meal, and they are delicious with butter; you can easily make up for all the calories you burned hiking!
Reservations required.