Adrienne,
I totally know what you are talking about.
The truth is that the parks have something of a weekly "seasonality" to how crowds flow to and from them. But now it is getting easier to 'guesstimate' what parks will be busy or light on a specific day based on several factors, like;
- Extra Magic Hours
- Special Events
- Time of Year (and in particular, if it is a busy, moderate, or light crowd size for that time of year)
These factors can in many cases outweighed that weekly seasonality. Also, Disney is using the Extra Magic Hours to help level out the park crowds, making that weekly seasonality less and less important.
Bottom Line: My bottom line for me is this. If I am there during a busy time of year, I avoid Extra Magic Hours, 100%. If I am there at a moderate time, I try to avoid Morning Extra Magic Hours, but am not so afraid of the evening ones. And during lighter crowd times, I embrace all Extra Magic Hours, as long as they suit my family's schedule.
I hope that this helps!
Have a magical vacation!