To be honest, i think the max value Steem should get to is 10$. More and even more more, would change the purpose of Steem and its Network. Bots will be taking over the Steem World, fighting a war against the simple User and every Chance to have a glance at the spot where the sun shines the most. It is a hard world, but a steem prize at 1000$ will have short term effect but affect the global life of everyone. No one will work anymore, they will write comments, just in hope to get some thousands of dollars for a pretty smiley or something like 'awesome post', wait that is still to long, just 'post' (yeah that seems right). Long term, the fall of Steem will lead to the fall of every other crypto currency.\
JK, but really, steem should not rise too high.
I guess the witnesses would decide to change the payout structure if that happened though to keep it from becoming a money printing machine for spammers?
I heard an interview with one of them a while back where they were talking about using their collective power to try and peg SBD near the US $ and allowing STEEM to rise to attract investors. If it stagnates then it will only be attractive to users of the system and not investors? Can't say I understand much of it but that's sort of what I got from it!