After you interview at a program, how much do your scores and grades matter to program directors? Is your interview impression valued more than scores and grades at that point?
It varies greatly from program to program. At some places the interview matters a great deal, at some places your academics remain the most important thing and the interview is more a formality to make sure you have a modicum of social skills. It's really not something the applicant should spend much time thinking about because you can't guess or control the parameters a program uses to make its rank order list. Focus on what you can control: Go on your interviews--be pleasant, show interest, smile, interact, thank the interviewers and the coordinators. If you want to be truly impressive, take the time to read the program's webpage and prepare some questions that show this familiarity. Then, at the end of the day, you know you've done your best.