My opinion is to keep your vote power over 70% as it makes your votes more meaningful to the author. Since Hive only has 3 decimal places of precision, if you run your vote power too low your vote could become worth less than 0.001. I think there was once a service to somehow help "dust" votes, and/or maybe somehow this has been addressed in one of the hard forks, but I remember it used to be an issue.

I do 50% votes because I follow a lot of accounts and I vote daily. I try to keep by vote power over 80% but it does occasionally dip a little under that. I also do 25% votes on almost all comments on my posts - people seem to like that. :)

In the end, do what works for you. Whatever your goals, I wish you well in achieving them!