My attitude has always been to vote the post, not the person, whether the post is from merlyn or Anonymous Monk. (For whom votes don't matter.)

I also am leery of "personality voting". That way lies feuds and grief which, while somewhat inevitable, is best avoided if possible.

But ultimately they are your votes. Spend them how you see fit. If you think that encouraging people who are not as active to try more often matters to you, then do that. If you think that voting on leaf nodes is important because you know that others will vote on the root ones, do that instead.

As for when you have "enough XP", my attitude was that I had enough when I had none, and I still have enough. People who are inclined to disagree probably would say that enough is getting onto Saints in our Book, which takes 3000 XP. After that there are no more titles, extra votes, etc.