Just had an idea in my mind: Homegrown team should have better teamwork and arena attendance.
Besides the merchadising, I think we should encourage managers to adopt the homegrown team. First they should have better teamwork, such as shout during the game with their own language, hand signals and eye contacts. This usually happens in reality.
Second, this should boost in arena attendance. Fans are easily to familiarise their players, and cheering team could sing their songs in local language. This would affect their opponents adversely.
Maybe it is difficult for the full team of homegrown players, I suggest to have a little boost in teamwork if the starting lineup is full of homegrown players. Hope more managers will spend their time and money on training players rather than buying/selling players.