Posts can only generate a payout from votes in the first 5 or 6 days. After that you can still up vote an older post or comment, you will lose the VP for that vote, but the recipient will only see the green triangle appear in Steemworld but no payout. Original replies to posts are ordered chronologically until the vote difference changes the order to the highest vote first.

Yes people still up vote replies and I'll be up voting as many of yours as I can. I think new replies are just that, new replies and open to receive a vote within the first 5-6 days.

You don't have to power up, you can use mine. If I didn't have other coins I can cash out, I would not have powered up Steem. Remember that it takes a minute to power up, but 13 weeks to power it back down.