Having a song stay in the same key isn't boring at all. It's when all your songs are in the same key that it gets old. Write a song in A Harmonic minor, and if you like the harmonic scale so much, write one in C harmonic major, it's the same notes with different roots. You can write a song in E harmonic minor too, if you feel like it, its different notes, but laid out in the same pattern on the fretboard.