If you have to spend to get to 5%, you are not hoarding right. On s11 I usually get to 1% without paying. On s10 i get to 5%. Only paying the monthly deal.
Hoarding is not a 'problem'. Hoarding is strategy and resource management. And this is one of the ways to play for free or almost for free. If you wanna donate or spend more to encourage development, feel free. If payment becomes necessary to play the game, more than 80% will leave. But imho, if all free players start paying, they will not work more on the game, because they will decide that everyone loves the game so much to pay so much, and they will actually do less.
Gree bought this game to make money, so the goal is do as less as possible to get as much as possible. Pure business.
This is one of the beauties of this game - you can be lazy and pay, or use your brain and patience. So the fact that you can't control yourself when you see the red or green dot, doesn't mean this is the case for everyone.
So if you see hoarding as a problem, you better look at what and how you do not to be able to get the same results.
If people hoard for more than a week, this means they are not playing every contest, which gives chance to people that hoard less or pay like you to get higher contest rank.
If payment becomes the only way to play, you will get to higher position only because players will leave the game.