I also read this as a minimum and not an absolute. Otherwise I don't see the point of putting "minimum" in all of those definitions -- surely you're not getting a bonus to reach EXACTLY 20 goals, so I read "20 goals minimum" as a requirement that the bonus number specified in the contract cannot be "3 goals" or "10 goals", it has to be 20+ goals (and so it can be "30 goals", or "25 minutes TOI/G").
I'm surprised nobody has mentioned Jason Demers yet. He was sent down to Stockton (ECHL) instead of Worcester (AHL) quite a few times in the past 2 years. Montreal media even interviewed him on such an occasion, asking him "has your play declined so much that you can't even make the AHL?" He was back up with the Sharks the next day.
As for the usefulness of the strategy -- suppose the guy who is sent down is making 1 million, and the team does that 10 times for 2 days each from the beginning of the season to the trade deadline. That guy's daily cap hit is $5,376 (1M/186 days), so the team saves $107,526. At the trade deadline this prorates to about $500,000 additional salary the team can take (*186/40 days left). Now triple that for Schenn.