If the reward pool gets smaller, won't it affect the curation award ?
Yes it will. Overall, everyone gets less. That is why I will not sell and am holding on to every little bit of Steem I get. Powering up just puts your Steem into a safer holding place (and gives you greater vote value). No harm there at all.
Keeping the SBD or selling the SBD, I wonder which is right at the moment !
ONLY if you want to sell or need to sell SBD, then now is a good time. Otherwise, as you said, it will go up more, so hold onto all you have. As for converting SBD to Steem and SP, you can try to guess when to do it, or just do it as you earn it and 'cost average' it. In other words, sometimes you will gain and other times you will lose, but overall, it will average out. If you try and guess, you may gain more or if you guess badly, you could lose more. It is a gambling game.
Yeah ! I hate gambling though. :D
I will take up your suggestion for now. :)