These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: "Another Suitcase In Another Hall", a song sung by Juan Peron's just-ejected mistress, which serves seemingly no purpose in the play plot-wise.
It's averted in the movie, as the song is given to Eva.
From a technical perspective, though, it does serve a purpose by allowing the actress playing Eva to rest before one of the show's most demanding numbers, "A New Argentina."
Casting Gag: Madonna, whose acting ability before Evita was critically panned at best and savaged at worst (with the exception of A League of Their Own), was cast to play a very famous celebrity whose inability to act was well-pointed out in the film. Thankfully, Madonna ended up acting far better than her character ever could, and turned in a performance that was surprisingly good to her, too. (Pun, if you know the score, intended.)