A better solution may be to make a progressively harder problem
I thought this was the whole point of the rising difficulty.
But I do agree rewards could be applied to more useful actions too, cleaning up is one of them. Right now what Bitcoin does is it mimics what banks claim to do, all it does is verify transactions are valid. This is needed because we don't really have it with fiat for example, but at the same time it alone has no value for long.
Bitcoin is just a medium of exchange, like fiat is, but blockchain technology has much more potential and when we understand that we also come to understand it's kind of a waste to dedicate all that power towards verifications alone.
Having said that, I still don't understand how a database is supposed to be kept secure without a considerable energy investment to analyze the data.
No, the rising difficulty of bitcoin is that each has goes from 1 in 100 to 1 in 1,000. So, you just have to do more of them. In this scheme, the little guy with a single computer gets left out , left in the dust.
What I proposed was a rise in difficulty of further hashes. So, 1 in easy, 2 is hard, 3 is very hard...
So, each person running a node, could easily do one hash. And thus it would become standard that everyone runs a node that can, because anyone can get lucky. Right now, if you are not doing terrahashes, you aren't even playing. (or, in other words, cars and bicycles need not apply, when racing rockets and supersonic jets)