by Kamakaze
The songs are nice but are definitely not mandatory to win. Many of my decks just don't bother with them, wasting one resource to play a card is often worse than just putting in a cheap card.If you have a 3 sphere deck with relatively cheap cards you won't really ever need too many of the same resource.
If you want to have more expensive cards in a multi-sphere deck then the songs can help (but so do resource generation cards)