Trisha:
From reading websites like www.touringplans.com which actually tracks information like this, I have found that evening
Extra Magic Hours don't have the impact on crowd attendance that Early Magic Hours has. Because our family typically opts to stick with the one-park-per-day
Magic Your Way ticket, we've typically chosen to stay in the park with evening Extra Magic Hours all day while avoiding the ones with Early Magic Hours, and that strategy has always served us well.
On the few occasions we've had Park Hopper passes, though, the time to transfer wasn't worth the effort if we were solely focused on enjoying as many attractions as we could. Even taking the monorail from Epcot to Magic Kingdom took upwards of 40 minutes. However, if you embrace the transfers as part of your total Disney World experience, especially if you're traveling between
Hollywood Studios and Epcot by boat or
Epcot and the
Magic Kingdom by monorail, a split park day optimizing Extra Magic Hours can allow you to maximize your time and ticket value.
Wishing y'all a magical vacation!
Whitney