Hubcaps is a great catch-all morning/afternoon restaurant. Their fare ranges from standard (eggs, sausage, bacon, et. al.) to impressive (strawberry pecan french toast, crepes).
Most of all, it's a slice of stability in the jumbled mess of restaurants that is Walnut Creek. It's not spectacular, but it's not supposed to be.
The atmosphere's comfortable, prices are aren't too high – though nowhere near Denny's – and the menu is so broad, you'll never get bored. There's something for everybody.
Having never been there past noon, it's hard to say how the lunch and dinner foods are, but it's not hard to imagine that it's palatable at worst. But breakfast is served all day, so don't worry.
Also, try the shakes. Mmmmm.