What does 我正好是诗情勃发 mean in the Chinese translation of Roald Dahl's Matilda (p.2)?
The original English (p. 4) of 如果那天我正好是诗情勃发 is:


  "Or if I were feeling lyrical that day."


Your breakdown is okay. 诗情 is a word of its own though, it is defined by ABC as:


  poetic sentiment


You might even make a case for 诗情勃发 as a single term.

Chinese translations of English works are notoriously bad in general and this translation doesn't seem any more natural.