All the people replying to you seem to be under the assumption that speed limits generally reflect the speeds most people find reasonable to drive in clear conditions. This is a very naive assumption to put it mildly.

That said, as someone who drives vehicles that don't exactly project an image of wealth I'd be perfectly happy with a scaled fine system since rather than getting singled out a fishing stop as a result of going 5-over in a shit car I would be more likely to be ignored in favor of someone who appears more likely to pay a larger fine.