It is absolutely unrewarding to be in a high league, you can choose some trade goods once a day, most of the time the once you do not need atm. or if your lucky 1 diamond.
the league bonus for a victory is 1000-1200 3500gold&food 1200-1400 4500gold&food.
Because battles are harder you loose too much troops, the league bonus or daily reward do not compensate at all
If you want to be in a ranking list, then you have a reason to collect medals.
Maybe nexon,BHG you can increase league bonuses like you increase prices of buildings.
above 1000 medals a league bonus should be 10000
above 1200 medals a league bonus should be 20000 and so on.
daily bonus is almost the same between 400 and 1400 medals !