I'm doing the same. I have both MoS and BvS Supes, but BvS Supes is going to be the last Cavill Supes I get for awhile. I'll be passing on the JL one because the suit looks like it's going to essentially be the exact same suit as the BvS suit. What I believe wil be the main selling point for the figure, is it will once again presumably be sporting an entirely brand new fabricated sculpt, being that he's again going to be sporting a different hair style. However, being I don't intend on getting many other JL figures from the JL film (if any), he will be out of place. Despite being a die hard Superman fan, I probably won't even get the potential black suited, "back from the dead" version because I'm attempting to avoid falling into the trap of getting too many variants of one character.
What I'll do is just wait for MoS2 because I imagine the suit will at least be a little different by then, and at the very least, they will recycle the same sculpt they use on the JL figure, so I won't miss out on that sculpt. Possibly even feature another brand new sculpt, which would be even better. I'd in that case get Supes and most likely whoever the villain is in MoS2.
BttF II Marty and Doc are coming out this summer, so I think I'd rather put my money towards those to avoid having a collection that is too superhero based, like you said. BttF II is my favorite BttF film, so I'd really like to have those two. I also don't have a Yoda in my SW collection, so I'd like one of those too.