There's the scene where in "Picaros" he puts on a record but this is mainly to drown out the conversation as he point out the bugs in the room. I don't have the book with me, but I think it is Castafiore's signature song and he describes it as his favourite.
Tintinrulz:
I don't think he thought much of opera, he probably attended more out of politeness than anything else.
I recall reading that Jacobs, himself a singer, did take Herge to the opera once, but the latter was not very impressed.
I've always felt the same about Castafiore myself. She is sometimes portrayed as so ridiculous: getting Haddock's name wrong all the time, inviting herself to his home for such as long time, bossing him around and being portrayed as silly and daft.
On the other hand, she is quite impressive in her handling of Sponsz in "Calculus Affair" and her defiance of the prosecutor in "Picaros".