I can’ do that, because lightnings are enemies, and they can only occur within waves (in fact, one of the bugs is that too frequent lightning can hold up the wave and prevent it from ending.
Currently, the only reason frozen environments are worth more is due to frost obscuring your vision. If weapons overheat slower, it would nullify the frost, so frozen missions would be worth just the same as regular missions (or perhaps, even less).
Fixed in v.54 
Bug
I’d like to keep them destructible because it provides an alternative way of finishing the wave.