I did a test once and found that if you do a nice cut and buff without getting crazy you only cut about 1/2 mil while two coats of high solids clear gives you about 2.5 mil. That extra coat is plenty as long as you don't cut too much off.
One of the tricks that I like to use is don't sand all the texture out with the coarser paper, bring it down close, but not all gone. When you switch to the next finer paper you are doing this to sand out all the scratches from the previous paper right? So why not leave a little of that texture and in removing the material that has the scratches from the previous paper you take it that little bit further removing all the texture. I feel much better doing this than removing all the texture THEN removing even more material to remove the scratches, get it? Try 1200 first, going down any coarser is often not needed and you are only removing material unnecessarily.