I was geeking out on David Bowie until about six in the morning. I've been thinking of 'Life on Mars?' and Procal Harems 'Whiter Shade of Pale' lately, the way that passionately sung gibberish is quite sincerely moving. And I think it's the way that these word-salad songs evoke confusion, remind us of just how hellishly painful confusion is to the human mind, painful to the point of tragedy really, and why we're all so willing to believe utter nonsense in order to avoid it.
Of course the melodies to these songs are great too. And maybe that's all there is to it.