I'm not sure personally. If they have fallen, I can't say I've noticed.
There will always be collectors and the collecting mindset will attach itself to something well documented - Peck, Freeman and Gouby were the pathfinders in that respect for modern milled pennies. They aren't solely reliant on the baby boomer generation for continued interest. Just as ancient coins were never reliant on people who were alive when they were circulating.
At the end of the day, I collect pennies because of the interest and multi variety and certainly have no intention of selling my collection, irrespective of value.