I suppose there's nothing requiring the proportion-curve for fines to be linear - but that might get silly and have other consequences. I guess the question comes down to value - finding something that the wrongdoer values (and remove it) that is in proportion to the damage to society they did. I would guess, that for the rich that we're talking about, time and/or freedom are more important than money.

The other end of the scale is interesting too - how do you disincentivise/punish for people who don't have any money and just aren't going to pay any fines you give them (i.e. the homeless)?

Then fine by Net Worth and not by Income. Fine by Tax paid. And made it like the Tax system the more you have the higher percentage.

There are people who just park their car anywhere and paid parking tickets, they really don't care because it was too small amount of money.

If anything, people should realise the level of inequality has become. How unfair and unjust the system has made against the bottom half of the population.

I don't think it's possible to find a fair solution that's purely financially based. On the one hand, the poorest members of society might be unable to feed themselves on even a $50 fine. Unless you propose to bankrupt somebody for a speeding ticket, there's just no way to make any amount of fine sting as much for the richest members of society.

Scale linearly to 5% of gross income before deductions, minus minimum wage/poverty line.

Then someone on minimum wage of $30k will just get demerit points while someone on gross income over $200k will pay $8,500. Given that their “taxable income” after deductions is around $80k they will feel that sting.

How about fine based on a small fixed amount plus an increased income tax rate for some time?