Take a look at the mess California is in before you go too far down the referendum-type path. Having a final veto power in the hands of the people may be a really good, final check. Imagine what vetoing SCoTUS decisions could be like.

It would have to be a high percentage (maybe even a true population majority, not just a voter majority). We certainly have the technology to make that happen now.

I'm still not sure we wouldn't wind up with the federal version of California, though.