Why are you farming? Do you have a target of cash or donuts you are trying to reach? I've played since day 1, have 500 million and just over 20k donuts, multiplier is about 2970% haven't spent a single dollar of real money, completely freemium. My point is I can now make as much money and donuts as I need that I don't have to farm as often as you say you're doing.
Get to a point in the game you're happy with and do just enough to stay there. New event? Spend those donuts then farm back to that level. Money isn't an issue at 2000% for you. It was taking too long to clear my town of cash and XP that I now only do tasks when I feel like it. Started to hate how long it was taking so cutting back (for me) has actually been awesome, still enjoy the game but don't have the huge time commitment I used to.
Find your happy level and stay there, too high a multiplier made my game less fun.
