With respect to your first point, I'm reminded of Peter Alvaro's comment "the only good reason to design a programming language is to shape your understanding of the problem". He points out that he was the only user of his first PL, but he had no regrets of about that, because it shaped all his later thought in his research.

From http://lambda-the-ultimate.org/node/5569 - Three Things I Wish I Knew When I Started Designing Languages. Alvaro's talk led to an HN discussion at https://news.ycombinator.com/item?id=19428433