One thing I was thinking about to still support people with very low-end systems is to let them turn off dynamic lights and force every mission to be sunny. This could work because as for now lights have no gameplay relevance. Of course, if I ever give gameplay relevance to it that would cause problems.
Sounds pretty good to me, even when it doesn't affect performances like in M&M 6, I've always hated weather effects, in M&M 6, for example, snow makes the pixel hunting (exploration) part quite tedious.
Being able to disable dynamic lights and weather effects should be a default option for every game featuring it.
And if you ever implement gameplay effects, just add a weather icon somewhere and link the gameplay effects to that icon instead of the weather effect itself, which could be disabled at will.