The attendance boost for newly promoted teams is real and substantial. It's not a guarantee of selling every single seat at any given price, but you can certainly improve your attendance income significantly when you promote. But the game does require you to sell 10000 seats in a 6000 seat stadium, nor does it automatically resize the arena when you promote.
I haven't been blessed with this "substantial" boost. Am I making more money than my prior division? Yes, but it isn't significant. I make the playoffs yearly and I am middle of the road or just below the league average for game income. When I increase capacity I have to reduce ticket prices to fill the seats. The net effect is zero or not much gain. I would have thought after the bump it would have been "substantial" and I certainly thought after making the playoffs on an annual basis I'd have no problem filling my small stadium and being able to expand. No reason to expand if you can't fill the seats. I have lowered my prices since division V. That makes no sense. That would be like a AAA teams ticket prices being less then the bigs - that doesn't happen.
In my crazy mind it would make more sense when I bump up that whatever I was selling my tickets for in Division V that I would be able to get let's say 20% more in the higher division. (That is less than baseball in real life for instance.) I would also have thought that I'd be able to expand aggressively and still make the 20% increase up to a certain seat count in expansion. So for instance let's say I have 6k seats in V, move up, increase ticket prices by 20% and then expand by another 2k without a problem selling tickets. From that point it would depend on results to sell more at the same price. Some scenario like this is what I am talking about.
Thanks for your feedback.