My last point was - high SBD price translates to higher rewards. So, if a upvote gives you $1 now (at low SBD price) that same user's upvote will give you more $1 when SBD price is higher.

Because of 50/50 split of reward, you get more SBD, if STEEM price is lower more SP, and you can also buy more STEEM with the newly earned SBD. This was the case in last part of last year and early part of January 2018.