Importance of hams, pies, bananas (8)
I believe the answer is:
emphasis
'importance' is the definition.
(emphasis is a kind of importance)
'hams pies bananas' is the wordplay.
'bananas' indicates an anagram (informal term for mad).
'hams'+'pies'='hamspies'
'hamspies' with letters rearranged gives 'EMPHASIS'.
'of' acts as a link.
(Other definitions for emphasis that I've seen before include "Stress, accentuation" , "Force" , "Stress or significance" , "Intensity of expression" , "Weight" .)