I don't know whether your heart ever necessarily changes, but time changes the way that you perceive the world. And you just hope it gives you more empathy and all those other things.
If you feel that you're not getting enough out of a song, change the instrument - go from an acoustic to an electric or vice versa, or try an open tuning. Do something to shake it up.
Each song has its own secret that's different from another song, and each has its own life. Sometimes it has to be teased out, whereas other times it might come fast. There are no laws about songwriting or producing. It depends on what you're doing, not just who you're doing.
What I always try to do is to respond to the song; I've always rebelled against theory.
I'm also getting an Ovation Legend, because I like them so much.
I actually spend as much time listening to new music as to old. Probably more. I just try to get something out of it all.
