Now this is very much a raw idea which popped into my head, so let's see where this goes.
To further reduce player turnover, daytrading and build personal ties with your favourite player, why not introduce a player loyalty bonus? Players which have been which have been with a team for say, 5 seasons, will benefit from a loyalty bonus in the form of a salary reduction of say...10%? Of course, if you want to translate this to RL you can say that after that period, he would have become popular among the sponsors and the sponsors are actually subsidizing that portion of his salary.
Any ideas to expand on this is much appreciated.