Man, no wonder you guys don't vote enough, you're seriously overthinking things...
- vote up questions you think are good
- vote down questions you don't think are good
The tooltips are just that: tips. They're not definitive, legalistic definitions of when you must up or downvote, they're just short summaries of the most likely reasons you'd consider a question to be good or bad.
Looking at the other answers, my thought process for voting up is similar to voretaq7's: if it's clear what they're asking and I think it's useful to myself or another professional, that's good enough.
For downvotes:
When reviewing, I routinely click on the questions I think are bad and downvote them (if they're not already) so that if they do get closed the auto-delete process will nuke them. But since unanswered closed questions only need -1 for the auto-delete to get them, there's no need to vote them into oblivion.
Redundancy between votes and closing is a feature: you want to close the really bad questions, but in the meantime you want them appropriately downvoted to show that they're bad.