Does it have any effect ? In FFXII weather would affect certain spells or is it just there because you know, weather effects?
I'm not sure if they said anything about superchargeing spells, but I kinda doubt it, though they did mention something interesting in one of their old game infomer videos about maybe you should be careful about throwing your chain at someone whose attacking you with an lightning spell.
Yes weather does have an effect on you and your party in DAI, it will effect both combat and exploration. Rain will create mud which will slow you down and build up over time on your party, if you're exploring in desert area's you may be hit by sandstorms which will damage you and force you to try and find shelter, blizzards will have a similar effect on you in certain snowy regions, and the other extreme weather would also likely effect you.