Easy Answer: GO!
I first went 2 years ago and we only stayed for 2 days, last year was 3, this year... perhaps 4...... but they were some of the best 2-3 days of my life.
There is plenty of "Good stuff" every day....
If you are craving the airshow part, yes some days are different than other.... but you will still see a chulk full airshow everyday of some awesome performers.
If it is all the other stuff, then any day is perfect (Perhaps not the last day).
I do recommend however to plan it out on paper to roughly know what you are going to set out and do, because if you aren't careful you will catch what I call Oshko****is and end up walking the lines of aircraft and taking 8,000+ photos like I did last year (But that was my objective so its all good)
Go when you can because it's WORTH EVERY SECOND!