The quote 'praise effort, not intelligence' isn't mine, though I probably should have used the word ability instead of intelligence. It's been born out of the numerous scientific studies done that continually show that by saying to a child 'I am very proud of the effort you put forth on X' as opposed to saying 'You're so smart! You studied hard and got a B instead of a C!' you are placing the emphasis on something the child has control over (their effort), over something which is innate (their natural ability).
I agree with you that learning to work hard is not a worthy goal on its own, but the praise effort vs ability debate isn't about encouraging a child to work hard but simply to praise them on what they have control over (their effort) vs their innate abilities.
Now, when it comes to child psychology and keeping a child engaged, maybe you're right and it's better to praise effort. But that should not come at the expense of praising intelligence; "intelligence" is the end product of many years of effort directed at the process of learning and thinking, not something that's doled out of a box at birth.
This idea of praising effort vs ability has been discussed previously here, so instead of repeating it I'll just link to it :)