[lotsofpulp]

The power law formula already skews the tax rate. There’s no need to further skew it with tax credits or other complications. If you want to adjust tax rates, simply modify the curve of the power law formula so that a given level of spending is taxed a lower or higher rate.

[scotty79]

Only of you have something to feed into the power formula and you don't unless you collect data more personal than what people are used to having collected.

Some people even object to paying with cards today because they don't want their transactions to be tied together to their identity.

So alternatives to power formula that achieve similar effect in different ways might be worth considering.