It would be fine if the type of pavement tile marked any difference in the rate of degradation of the tile.

I'm not sure what you mean, can you elaborate?

Worse pavement, maybe, must degradate faster than best.

I'm still not sure what you are asking? However there are already ways in which "better" ground tiles degrade to slightly worse tiles. For example the following tiles degrade into each other instead of degrading completely: asphalt => concrete -> stone-path -> ground.

Ah! Ok! It's better tan I expected. I'll install your mod :)