Lately we have been going for long weekends 3 or 4 days and we can def do it in that amount of time and that usually means CROWDED but my preference is 5 days. And that usually means enough time to do ALL the rides I want many times over and still have plenty of down time to sit and smell the roses. I like to have days where I can just sit back and relax and people watch or sit and enjoy and ice cream cone or a cup of something to drink and just relax. Sometimes we like to take one day to do things we normally wouldn't have time to do like look at shops, go to Pirate Island, go on rides we normally wouldn't take the time to etc. When you have fewer days you tend to only do the "big" things so you don't "miss" out on anything you want to do but when you have more time you can do those other things.
For example on our last trip we focused on things we had never done like Golden Horsehoe and seeing the Billy Hill show (which we very much enjoyed and am now going to take my mom to see! on our trip next month) and then going to Golden Screams (which my daughter ended up winning!!) things like that!