I think some of you haven't thought about the obvious.
The first and biggest impact would be one helluva stronger labor movement early on. Historically the SCOTUS almost always takes the side of elites, esp the wealthy and corporations, and was one of the biggest obstacles for unions. The Warren Court was an aberration likely to never be repeated.
You'd see an end to using injunctions to break strikes, an end to charging unionists on trumped up conspiracy charges, and even the occasional prosecution of union leaders for treason, no less, just for seeking better wages.
All of this couldn't help but spill over into more rights for nonwhites much earlier on. Imagine A Phillip Randolph or Emma Tenayuca as much more powerful figures, for example.
Without SCOTUS standing in the way for the past century, you may even see labor as powerful in the US as it is in much of Europe.
As for the role of money in elections, has it occurred to some of you that would be one of the very first targets of a popularly elected SCOTUS? I have a hard time believing we wouldn't have seen campaign finance reform judicially mandated, probably well before WWII at the latest.
On another bright side, many of the mediocrities and stealth candidates for justices would've never made it far. No doubt parties would choose their best and most accomplished, or at least those with name recognition. No Clarence Thomas, no Souter, etc.