When ever I hear this line, I imagine Joni watching some old rerun of say the Donna Reed show, or some other classic 50s/60s family sitcom. Father Knows Best - that sort thing. The idealized family portrait. It has always sounded like a follow up to Song For Sharon to me, where as a little girl, she has this dream of getting married, and living a 'perfect' life. As she grows up, her goals change, and she realizes that she was just chasing dreams. Then while watching TV one day, this rerun comes on, and she flashes back on how that ideal used to appeal to her. She no longer aspires to that vision of life, but seeing it again on TV, she's some how haunted by it.
To me, what's so powerful about that short, simple line is that it can apply to so many situations. Who hasn't had dreams, ideals, or ambitions that at one time seemed unshakable, yet over time you either out grew them, or even worse, simply abandoned them. I have no idea if this is what Joni actually meant, but I get goosebumps every time I hear this line. Jack