Strange for vacuous elite to be productive (7)
I believe the answer is:
fertile
'productive' is the definition.
(I know that productive can be written as fertile)
'strange for vacuous elite' is the wordplay.
'strange' indicates anagramming the letters.
'vacuous' says to hollow out the word (remove centre letters).
'for' with its middle removed is 'fr'.
'fr'+'elite'='frelite'
'frelite' with letters rearranged gives 'FERTILE'.
'to be' is the link.
(Other definitions for fertile that I've seen before include "(Of soil) richly productive" , "Able to reproduce abundantly" , "Fruitful" , "Rich in resources" , "Fecund" .)