I think the suggestion of tying the upvote to an endorsement may be a bad idea. It would be conflating the fact that you want the comment to be seen with the possibility that you might agree with it. The comment could be tangential/adversarial to your opinion, and so you might not upvote it, however it could still add to the discussion, and hence you would endorse it.

To answer your second question I believe pg has stated that only users with over 10000 karma have their comments automatically endorsed.