Fog Cloud plus a lightning spell also has a special effect. And Plant Growth plus a fire spell. I can’t think of any other combos off the top of my head, though I’ll bet there are some.

I also like the idea (despite thinking the wet + electric combo in particular is too overpowered and should be toned down) but I know these combo effects can be divisive when they diverge from 5e RAW.

"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"