It's worth catching show rehearsal (8)
I believe the answer is:
practice
'rehearsal' is the definition.
(thesaurus)
'it's worth catching show' is the wordplay.
'it's worth' becomes 'price' (price is a kind of worth).
'catching' is an insertion indicator.
'show' becomes 'act' (act is a kind of show).
'price' going around 'act' is 'PRACTICE'.
(Other definitions for practice that I've seen before include "''. . . . . . . . maked perfect''" , "Exercise; professional business" , "The exercise of a profession" , "It makes perfect, 'tis said" , "Routine" .)