A big problem in the past with Grad Nites in DCA, was that lots of Grads wanted to watch the fireworks. The Grads made the viewing extra crowded. But this year with fireworks being at 9:30 in May and taking 15 minutes, and the Grad Party starting at 10 this may help. Many the grads will want to get into DCA earlier and give up on watching the fireworks.
World of Color on the other hand requires a FastPass to get into the reserved viewing area. So regardless of the crowds it can't be busier. They run at 9:15 in May and then 9 when it starts going twice a night with Memorial Day Weekend. The problem with WoC is when it ends you are in a crush of people wading to the park exit.
One things to keep in mind about the Grads is there are not a lot them. They have several thousands guests and you are part of 20-30 or more thousand guests. You just see little groups of them allover and are rarely surrounded by them.