My criteria for upvoting are
- is it ontopic
- and is it of good quality (clear and understandable, a real question)
- and wasn't already asked (here on the site!), or is it better as the duplicate
Spelling and grammer is not so important, because this can easily be corrected by us, in contrast to the content. Seeing research effort doesn't matter much for me too, as long as there's effort in making a well written and focused question: even if something might be found in big reference manuals or via google in some Internet forums: we could possibly do it better here.
It's easier to see if a question is good, than to see if an answer is correct. So I guess the upvoting questions barrier would be lower. Want to see more such questions? Upvote!
- it really answers the question (isn't like a comment or a guess)
- and is written so that it's understable
- and it seems to be correct for me
- and it's contains an explanation, not only a solution
Again, spelling and grammar can be corrected and don't affect my voting.
I rarely downvote, only if I see that it's really wrong, bad, or intentionally off topic. In some cases it's better to flag it (off topic, too localized or duplicate question, meaningless answer).
Finally, I would say: vote often! Seeing votes ranging let's say from 0, 1 to 10, 12, 20 and more votes, tells me more about quality than seeing a hundred Qs and As with 0 or 1 upvote. And feedback by upvotes is a very good motivation for users to continue posting good quality.