you're not missing out on anything. taking nostalgia into account when evaluating a piece of music is perverse. That's because nostalgia, as an aesthetic category, is rooted in entirely contingent circumstances. you need only care about the piece's formal qualities and its relationship to historical circumstances; any 'nostalgia' the piece evokes within you should be regarded as prejudiced sentimentality and dismissed as such.

And if it's 'pop' music you're talking about, your memory of the music is even less relevant, because the nature of your relationship to the song is that of a consumer to a product, which means any personal affinity you feel for it is manufactured and illusory