Yeah that would be useful, but it should just be a key like alt that you press to see enemy mana bars. Otherwise they might end up crowding the screen with hp/mana bars ><. Still I'm not exactly excited about the idea, if it's important to know if my enemy can use a spell I just click on their caster/hero but most of the time it doesn't matter I just have to be ready to counter it.
There is something because otherwise there would be nothing, that should answer all your silly "why do we exist?" questions.