> Is it worth validating (upvoting) a listnerd mail linked to a daily blog? Is it more valuable to you being sent off chain or to another HIVE user's content?

It really depends on what each thing is.

I have read daily blogs that are really 30 words long once you take out the usual stuff they copy and I have read ones that are of quality and are actually long and you can see the effort in them. I have seen mails that lead to great business and I have seen those "Make 38 billions a day by signing up". 

I mainly just upvote posts I like or see that effort went into them. I skip voting mediocre posts but downvote lazy content instantly, I think having those are an insult to people like you that they get upvoted the same rate you or anyone who work on their content would.