Decorated too much, quite fairly (6-6)
I believe the answer is:
pretty-pretty
'decorated too much' is the definition.
'quite fairly' is the wordplay.
'quite' becomes 'pretty' ('pretty' can be a synonym of 'quite').
'fairly' becomes 'pretty' (I've seen this before).
'pretty'+'pretty'='PRETTY-PRETTY'
(Other definitions for pretty-pretty that I've seen before include "Knick-knack; over-dainty" , "Twee" , "too cute" .)