The 1st weekend of October WILL be busier with Gay Days and UEA (yes I know not ALL Utah schools will be out that weekend). We were there Saturday of D23 Expo and it was surprisingly quiet. It was actually busier on Monday after the expo.
It will most likely be PACKED! With the new Halloween stuff going on, for only a few weeks, the locals will be out in droves! If you go with a few priorities in mind, and do not expect to get to everything in the park, you will still have a good time.