I agree with Dr Ben. I've also been a big fan of KD's since several years ago when he did the slow headspeed work with the Hughes 500 Logo.
I've wondered the same thing you are over the years. I really think working on perfecting the fundamentals allows you to do anything you can imagine. Music helps. I often find that while working on a specific maneuver that I will accidently "discover" a variation I hadn't thought of before. Something really basic I just started practicing a few days ago is a flip? that instead of going to 12, 3, 6 or 9 for a pure flip or roll I take the cyclic stick to one of the corners ie 1:30, 4:30, 7:30 or 10:30. If I'm very careful to give zero rudder and just vary the collective this move gives an interesting, to me anyway, tail excursion from centerline that will return it to the original heading after a full roll/flip.
I also watch for the feeling that my flying is becoming repetitive doing only the moves I'm most comfortable with. When that happens I force myself to stop and start focusing on something I'm not comfortable with. Keeping some notes on things I've either mastered or am working on helps me to keep from forgetting various moves and transitions.
Breaking down basic maneuvers like a loop I try and ensure I can do them in all orientations and flight directions. For every basic figure of aerobatics you can add piros, flips and rolls in all directions. I call these compound maneuvers. Doing this means you have a virtually unlimited library from which to pull.