It sounds to me as though you're saying that Spotify's loudness normalization is affecting the audio quality of the records. I don't believe this works the way that you may think it is working.
While Spotify IS applying file compression (ala mp3) to every one of their records (and this affects the sound quality) I have not heard any reports of them applying any additional post-EQ or volume compression in the way that, say, a radio station might. I believe you may be mistaken as to what the Loudness Normalization feature is doing.
It is simply turning down the volume of tracks that have been mixed/mastered to excessive loudness levels so that they match the average loudness of more sensibly-mixed/mastered songs. Turning the volume of the louder track down has no effect whatsoever on it's audio quality. The meta-effect, then, is that the normalization disincentivizes the practice of mixing/mastering songs too hot; something which DOES have a negative effect on the audio quality of a song.
