I didn't address that because there's even LESS point to bringing him in if you proceed from there. The only thing that makes Plagueis even remotely tempting as a name (because he's not even a character) is the tie to Palpatine and his past. Erasing that tie means you might as well come up with a new character. Which they did. And again, Abrams/Kasdan didn't even reference the old EU. They're not looking at it for inspiration at all. Strongly doubt Johnson is, either.
Whether by coincidence or not, there's a lot of things in Force Awakens that show up in the EU. So if by accident, or if they happened to cherry pick ideas they liked, there's definitely EU influence in Episode 7. You can't just stick your head in the sand and pretend Lucasfilm isn't going to cherry pick all these great ideas that work that have already been written.
So what's Kylo Ren, then?
Kylo just murdered Han Solo. We're supposed to backseat this dude (maybe one of the more interesting portrayals of a bad guy in Star Wars, period) so we can dive deeper down the dumb Prequel rabbit hole so as to beef up a bad guy for the sake of what - making Palpatine weaker/dumber? Retroactively making the Prequels seem more important?
Again, what would Plagueis actually add to this story (especially the first chapter as we've seen) that would make his resurrection from being mentioned in one Episode III scene so much better than simply developing Snoke as a unique character?
I have no complaints with Snoke being an original character, but the implication of him being Plageus, and if they do borrow from the EU, means a return for the Sith and abolishing the rule of 2. I hate the idea of there being just two Sith and up until the prequels, a legion of Jedi. I want the story group to explore the idea of a team of Sith vs a team of Jedi.
Just like you say "why would they do it to boost the prequels, new trilogy doesn't need it"... it doesn't need it. But no one outside of Lucasfilms and Kathleen Kennedy, those in the know, know how well Snoke/Plagues fit in this new trilogy. At the VERY least, we have no idea how well he'd work because we have no idea how this ends. So you can't say it's a terrible idea because of your aversion to the prequels. Only a Sith deals in absolutes, let's keep an open mind here.
I don't get this particular argument... Plagueis was the Emperor's former master. That all the audience needs to know and that's all there IS to know. This would be stated in literally one line and it would be enough.
They literally don't even have to lol... they could just be like "I'm an ancient Sith, better known as Plageus the Wise" Done. Anyone who wants to remember the prequels, can do it. Everyone that wants to ignore them, can continue doing so.