A penny for your thoughts is a terrible deal considering they are worth two cents.

Your thoughts are worth the one cent people are willing to pay, not the two cents you think they are worth.

A penny when solicited. Two cents when given unsolicited. This is clearly showing a supply and demand relationship.

Shower thoughts are ten-a-penny

The metal in a penny is worth more than 3 cents though, so it would be worth it if you are willing to break the law

It's worth double ( to this scummy advertizer economy ) for a chance to persuade others, than to get their input