Looking waaaay ahead to Summer 2016 and wondering what thoughts are on spending a day at both TL and BB on an 8-day June trip. Note that the summer heat burns us out, so we’re not looking to spend everyday in the four main parks. Thanks! 
Are you staying at a Disney resort? I would plan 2 days MK, 1 day AK, 1 day DHS, 1 day Epciot and then one more day returning to a park that you like / want more of. That makes 6 days. You need one not in the parks day - or at least I do. That leaves one day for water parks. I do both water parks when we have at least 10 days. And we go all the time and don’t need to repeat parks as much because of it.
Both water parks gets to be a lot!
I would. We plan rd at each park, then rd at each water park, then fill in with whatever else we want to do. We go a lot, though, so we’re not under pressure to do every attraction.