Hi Kara. Visiting parks that host Extra Magic Hours is probably one of the more debatable topics. For what it is worth, I will provide my recommendation as this is my personal approach to Extra Magic Hours.
In a nutshell, I try to take advantage of this feature in the Morning, but not as frequently in the Evening. My family and I are early risers and can reliably get to the park the hour before typical opening hours when the morning Extra Magic Hours takes place. This allows us to typically get on 2 or 3 of the best rides before normal park hours open. Especially during more crowded times of the year, this can be a big time save. However, unless you can take advantage of the full hour, I don't recommend going as this park will tend to be more crowded afterwards. If so, we sometimes choose to switch parks afterwards.
As for the Evening hours, we have used this feature three times at various parks. We have tended to find this to park to get really crowded and lines for rides can be quite long. While crowds thinned out towards the end, we now usually choose instead to visit a different park or use this time to enjoy a nice dinner. So, overall it may be a good idea, but the key is to make sure you do take full advantage of the morning hours and not arrive late. Hope this helps!