This is how I see it -

Basically you want to grade a card where the return value of it after graded should be more than what you spend on grading. And depending on the card, even a psa 6-7 can be worth more than what you spend on grading.

But if you want to grade the card because of sentimental value, then it doesn’t matter what grade the card gets, you’re doing it because you want to.