"Is this important?"
“这是重要吗" got denied on 2019-06-10. Didn't report, because I'm not certain. Came for this question as well.
What is the reason that the adjective zhongyao doesn't seem to require hen before it like most Chinese adjectives?
Actually, it's not required to include 很, which is the common linkage between noun and adjectives. As long as you are not including extreme before the adjective, the sentence still makes sense without 很.