Here's a better idea to think about. Allow users to power up their vote above 100%, at the cost of destroying their vests permanently. Like a dragonball Z style Kaioken.
So lets say i want to double the power of my 7000 vests and cast an 8 cent vote on something that i think is important. I can do so by destroying a certain percentage of them (maybe like 1% for a double, 2% for a triple, something along those lines... with the ultimate weapon of sacrificing all of my steem power for a 100X keioken. )
ALso, id be giving others extra SP incentives without creating more steem. And we can have fun watching mega-bernie-sanders and mega-dan go at each other.
What we really need a sink for is vests.