The club are only missing out on revenue if they are holding back the seats, not sure why they would do that. If people have bought tickets and not turned up, then the club might be missing out on revenue, but maybe not. I go to most games and spend nothing but my ticket with the club.
The Psychological element. Where is your evidence that a full stadium makes others want to attend?
Surely its game and the atmosphere that attracts people. That would mean its not the empty seats that are the problem , but the full ones that are occupied by quiet fans.
If you are correct and a full stadium attracts more fans, then that might be a good thing for the club bit maybe not for the fans. If more fans are attracted to the club then the demand for tickets goes up and that almost inevitably leads to an increase in price for those tickets (which is where the advantage for the club comes from) I am not sure higher prices are an advantage for the fans.