Fan attendance is an approximate measure for how popular a team is and how much money it should expect to make in a year. Therefore, if a team invests more in expensive or, presumably, higher quality players, fans would seem to appreciate the front office efforts.
Aside the 4 points on the far-right of the graph, there is a pretty good positive trend, supporting the assumption that money buys better players and more fans.
Getting back to those four dots - this is interesting as they represent Seattle, which has the very largest fan base but an extremely low salary base. What is the lesson to be learned for other teams (aside from more fans is a good thing)?
And some gratuitous fan video: