I really like the thematic idea of changing the music, as well as boosting a creature for a turn like that. I wouldn't include this card itself towards the +2/+0, unless you already had one in play and played a second one; then you'd get one from the one already in play.
Two issues to consider though are 1) whether this should be stackable and 2) whether this should include pillars/pends. Imagine having 3-4 of these in play and then dropping 5 pillars from hand... that's a lot of damage to surprise someone with!
You could expand the idea of the anthem series to allow only one anthem per side, or perhaps a limit of one anthem of each element per side (or both sides) such that if you played a second one, the old one would be destroyed. (like weapons/shields) This makes thematic sense because you can't sing two songs at the same time. (I can't even sing one, but whatever...) For other elements, you could have life gain, poison, bonus quanta, mutation, delay, debuffs, etc.