If author said something that you do not understand because of complexity of a matter -- then upvoting would be right decision.

Oh dear. Hopefully noone else feels this way. Would you upvote such posts?

If you don't understand, then the right thing to do is reply and ask for clarification. If you didn't understand, then you're likely not the only one. If the author can explain the matter in such terms that you understand his previously opaque posting, then go ahead and vote it up.

Anything else would equal going around going "wow, this guy uses big words that make no sense to me, he surely knows more than me".