Does it bring anything new to the table to warrant a possible purchase?
Yes. I agree with Thales01 on his comment.
I think you'll be able to play Imperial Settlers with more people, kids, casual gamers etc. 51st State line of games will be for more interested players and pos-apocalyptic theme fans. That's exactly why I'll buy Imperial Settlers (Essen or sooner?) even though I have everything from 51st State including Ruins.
It's similar game but I will play both with completely different people - example: my girlfriend don't like 51st State for its' grimm theme but she's willing to play Imperial Settlers because the theme reminds her games like 7 Wonders where you're building your empire and it doesn't look so aggressive.
with a small exception - I won't be buying Imperial Settlers soon.
Question from thread subject is sligtly different:
Do I need this if I own 'New Era'?
Maybe... But there is no NEED, unless some of Thales01's arguments concern you.
I have 51th State,New Era with all expansions and promos, and I haven't played it enough yet. And according to my New Year's resolution - I won't buy next game which falls under Johnson Theory(i.e. duplicates another game gameplay) before getting rid of already owned game.
But 51 State system now is superior in total card number and portability and I really don't have anything against the theme. So I don't NEED Imperial Settlers.