Log onto Super Mario Run right now and you will be greeted with an event known as Loads of Coins. Between now until 25 January 2017, you will receive 1.5 times the usual amount of coins when you beat the Toad Rally, so that will help accelerate your farm.
https://www.youtube.com/watch?v=Qpdfg5km60w
With the absence of new content at the moment, it makes sense for Nintendo to pull off something like this to draw in the users, much like what Pokemon GO is doing right now. In any case, the event is live now, so take advantage of it as much as you can.