If you haven't got that many AAs yet and need to distribute the next carefully for max effect, i'd suggest to hold off a bit longer until buying the next levels. Sure VP is nice and the higher levels add a bit of reliability (not much with additional +10 and +20 modifier to be honest). But from your post it sounds, that you have more important AAs to get first.
However if you use VP in critical CC situations, use it with MD/PD as adviced (depends on the situation which one you will want to use).








