The value of a post will go down as the reward pool is delegated out throughout the day. If you are not getting any more big votes and other posts get them your posts value can go down as time goes on until payout. If other posts are not getting votes the value of your post can also go up.

Your voting value is derived from the amount of Steem Power you have, more steem power = more voting value.

No, your votes never hurt anyone. Only a flag can hurt someone else.

Yes, just acquire more steem power. Whether that be from posting, networking and earning it through hard work, or purchasing it on the open market.

The value of a vote is derived from the steem power of the voter, some posts get a lot of votes from people with very little steem power, so the money effect of those votes is small.

The inverse of my answer to 5, those posts got voted on by people with more steem power. If a big steem power holder votes on your post it is awarded much more.

Vests are another name for Steem Power

It only influences how many people will see your post, in their feed. The more followers you have the less extra networking you need to do to get noticed. That doesn't mean you should take your followers for granted, you shouldn't you should still be out here every day interacting with people and trying to show the community that you care, and are a cool part of it!

You can, but absolutely should not. Its frowned upon. You already published it, do you see websites re-publishing their content all the time? Nope, once its out there its out there. You can always link to older posts if they are relevant in new posts though. Like as a " Hey check out this older post of mine you might like if you enjoyed this one!" sort of way.