Fan factor has a huge effect on the game of bloodbowl. It may seem like a waste of money, but on average every 10,000 you spend on fan factor will be re-earned in 6 games (of course it's not quite this simple, but not far off).
You don't need fan factor 9, anything above 5 is pretty good - use it to even out your spending so you make the most of your starting cash.
The extra money you win is very important to teams with expensive and/or fragile players, such as ogres (expensive), halfings (fragile), and elves (both).
Fan Factor also affects kickoff table rolls. Four off the 11 kickoff table results are affected by fan factor, so whoever has the higher fan factor is more likely to get a beneficial result.