Is reflecting upon a choir conducive to the path of Enlightenment? A few years ago, I read in the introduction of a Spirituality book about this story of Gautam Buddha. I've forgotten the name of the book, but this poetry has stuck in my memory for ever. The story goes something like this:

The young prince Siddhartha is sitting in the garden, having felt disgusted by the vanity of the celebrations going on in the palace. That's when he hears a group of celestial beings passing by singing melodious choirs:


  We Know not whence we come,
  nor where we float away
  Time and again, we tread this round, of smiles and tears
  In vain we pine to know
  whither our pathway leads
  And why we play this empty play  


Each time I remember or reflect upon this choir, I get a profound feeling of anicca. I know that even thinking about this is also a sign of attachment, as even those thoughts are impermanent. But is it wrong to get energized or inspired by a choir, even if the inspiration is towards the path of enlightenment?

As a side note, has such an anecdote really happened with Gautam Buddha? Is there such a mention in any suttas?
"But is it wrong to get energized or inspired by a choir, even if the inspiration is towards the path of enlightenment?"

In principle, I don't think so. It's quite reasonable actually to regard the verses in the suttas having that precise purpose (otherwise, why write in verses?). Additionally, many traditions do chanting.

"I know that even thinking about this is also a sign of attachment, as even those thoughts are impermanent."

Not necessarily. Inspiration does not entail craving, and feeling inspired is very important, I don't think anyone who have directed their lives to this path would be able to gather energy to do so without inspiration.

Moreover:


  [...] and he gains inspiration in the meaning, gains inspiration in the Dhamma, gains gladness connected with the Dhamma. When he is glad, rapture is born in him. in one who is rapturous, the body becomes tranquil; one whose body is tranquil feels pleasure; in one who feels pleasure, the mind becomes concentrated.
  
  --   Vatthūpama Sutta, MN 7


also:


  This was said by the Blessed One, said by the Arahant, so I have heard: "Endowed with two things, a monk lives in ease in the present life and is appropriately aroused for the ending of the fermentations. Which two? A sense of urgency &amp; awe toward things that should inspire urgency &amp; awe and, feeling urgency &amp; awe, appropriate exertion. Endowed with two things, a monk lives in ease in the present life and is appropriately aroused for the ending of the fermentations."
  
  Feeling urgency, awe / toward what should inspire it / the wise,  masterful /
  ardent monk / should investigate / with discernment. / One who lives thus / ardently / not restlessly, at peace / committed to awareness-tranquillity / would attain the ending / of suffering &amp; stress.
  
  -- Iti 2.10


However, as we know, it's not always like this:


  Bhikkhus, have you not known me to teach the Dhamma in such a way as this: ‘Here, when someone feels a certain kind of pleasant feeling, unwholesome states increase in him and wholesome states diminish; but when someone feels another kind of pleasant feeling, unwholesome states diminish in him and wholesome states increase [...]?" — "Yes, venerable sir."
  
  -- Kīṭāgiri Sutta, MN 70


By "inspiration", we are presumably talking about, say, something that acts as a vehicle to something else. But when it ends in itself, that is just sensual delight:


  And what, bhikkhus, is the nutriment for the arising of unarisen sensual desire and for the increase and expansion of arisen sensual desire? There is, bhikkhus, the sign of the beautiful: frequently giving careless attention to it is the nutriment for the arising of unarisen sensual desire and for the increase and expansion of arisen sensual desire.
  
  -- SN 46.51


In more detail:


  "Monks, in whatever monk or nun there arises desire, passion, aversion, delusion, or mental resistance with regard to forms cognizable via the eye, he/she should hold the mind in check. [Thinking,] 'It's dangerous &amp; dubious, that path, thorny &amp; overgrown, a miserable path, a devious path, impenetrable. It's a path followed by people of no integrity, not a path followed by people of integrity. It's not worthy of you,' [...].
  
  -- SN 35.205


That is, craving through the five aggregates.