I'm a die-hard baseball, have been since I was 8 years old. I value the tradition and acknowledge the average fan needs to be younger. I think it is a little more complex than what you laid out (thought I do appreciate you ananlysis) and it relies on a bunch of factors. https://www.forbes.com/sites/maurybrown/2017/11/22/mlb-sets-record-for-revenues-in-2017-increasing-more-than-500-million-since-2015/#2a8a2c9d7880
Revenues are increasing in baseball. The TV Contracts are bigger than ever, they embrace ditial distribution and marketing more so than any other Major League sport, and because of it's somewhat wholesome nature, they can rope in HUGE sponsorships.
What I am saying is the money is there. I think they need to focus on promotions like you said in your individual angle, and ways to expose the game to younger kids. The lack of people allowing their kids to play football will help direct them to less concussion-prone sports like baseball, but that is hwere it starts.
Once you fall in love with the game, you're a fan for life. No need for drastic rule changes, MLB just needs to spend this money to expand little league and get players more involved.