I heard Steven James speak at a recent writer's conference. At one point, he said, "aspiring writers are often told to avoid writing themselves into corners. No! It's by writing your way into corners and then figuring how to write your way back out that you produce the best stories." He then proceeded to reel off several examples from his own writing. Yes, some ideas just don't work. But before abandoning the project, know why it didn't work.
Empathy is a great skill or character trait to have as a writer. With Empathy you dont have to actually feel those emotions, you can imagine them and put yourself in your characters shoes. I think if you seriously lack empathy then yea i can see why you would have to be in a certain mind frame to write properly. I have empathy though.
Ah, well, let's see...I still think of myself as young. Handsome? Of course!! Tall? I'll get back to you on that. Full head of hair? Sure (thinning hair, that is). Plus, his wife comes from the same part of New York that I do. And he wrote a great book on writing. So, he passes muster.
I was speaking in general however OP made statements that when he's in a certain mood that's how is writing comes across. So if you can only write in the mood you are in, to me, it says you can't empathize with other feeling in order to write those well without having to experience it yourself.