Intensity of Spanish port user on vacation (6)
I believe the answer is:
vigour
'intensity' is the definition.
(vigour is a kind of intensity)
'spanish port user on vacation' is the wordplay.
'spanish port' becomes 'vigo' (I've seen this before).
'on vacation' suggests removing the centre.
'user' with its middle removed is 'ur'.
'vigo'+'ur'='VIGOUR'
'of' is the link.
(Other definitions for vigour that I've seen before include "Active strength of body or mind" , "Stamina" , "Energy, pep" , "Great strength and energy" , "Physical strength and health" .)