Crit frequency

For games where success with added benefit on certain rolls is part of the design what feels like an appropriate ratio. I'm using the terms crit and hit, but I'm not specifically talking about combat. This is essentially 3 questions.

What us the upper limit of crits per roll for crits to still feel like a special occurance and not just a common result?

What is the upper limit of crits per hit for regular hits to not just feel like a lesser crit?

What is the lower limit of crits per roll where taking actions that would require a crit to meaningful impact the situation would be worth considering?

Obviously this is a question about feel, and any answer given could be met with designs that break the guideline to great success. Just trying to hone in on some suggested boundaries for crit ratios for the more typical kinds of chance based crit.