I sometimes do this, too. I've always thought that it'd be cool to get a DLC (for which you'd have to pay, but...) with which you'd be able to switch between ACNL and ACCF/ACWW music going to the Settings menu in the start menu.
I hate new leaf's soundtrack... But i am also not a big fan of the new leaf game so i don't know. Anyways i can never tell which one is better.. wild world soundtrack or population growing.