That last one feels like an extremely unsafe assumption, to the point that I would strongly advise against spreading it around. The Republican hardcore ALWAYS shows up, and they ALWAYS vote in a straight line ticket. That's been the rule for the last 6 years, and I think we should be examining 2018 and 2020 with that in mind.
Our chief objectives should be threefold: resurrect the state parties so we have candidates for every race, excite our base, and figure out a way to overcome voting restrictions. Don't even think about driving down Republican turnout, there's never going to be a decent reward on investment there.
It's a bit of a different situation with Republicans controlling everything.
I wouldn't spend a ton of money driving down Republican turnout, but fire needs to be met with fire. We know Trump's RNC will probably be targeting FB ads to get Dems to stay home.
There also needs to be money put into researching the best methods to get your average Fox News viewer/talk radio listener/Breitbart reader to kick the habit.