I think it's a bad idea, as endlessly raising crop quality is diametral to the goal of an eternal world.
IMHO it would be better to give them a ceiling that one can push against, that will push back harder the farer you already stretched it - so grinding harder would still give benefits compared to the ones that grind less, but we won't have to explain to new players some day that the quality difference between two q12.01M carrots can be quite huge...