I've noticed this in all arts. It falls into 4 categories - I like to call them Elvis stages.
1. Beginner/apprentice - Sun Elvis. (Just starting out, lots of enthusiasm, inventive, but still learning how to apply the talent.)
2. Journeyman - Middle Elvis. (Talent has been channeled with skill, still lots of creativity, period of high productivity. Most of the best works created here.)
3. Master - Fat Elvis. (Skills perfected, creativity waning to gone. However there can still be a burst of creativity, leading to a creative gem. But don't bet on it.)
4. Empty husk - Dead Elvis. (Creativity dead. Talent dead. Skills meaningless, with nothing to work with. In the writing world, collaborations between Big Name and Little Name, which actually are Little Name ghostwrites of Big Name stuff.)
It holds across all arts...
I've learned over the years that when a artist reaches Fat Elvis, just write them off and go look for a new beginner/journeyman...