I think you should keep it simple. I also think it's wise to write the thank you notes right after the interview. If you wait to go home and write the note, then mail it out, it might be too late. You want them to have it right away. Give it to the front desk person or something.
Would it affect your chances of getting in? I highly doubt it, because after the interview, they are done and have nothing else to do with the admission process.