Positive quality luxurious for the most part (4)
I believe the answer is:
plus
'positive quality' is the definition.
(I've seen this before)
'luxurious for the most part' is the wordplay.
'luxurious' becomes 'plush' (I've seen this in another clue).
'for the most part' means to remove the last letter (most but not all of the letters).
'plush' with its final letter taken away is 'PLUS'.
(Other definitions for plus that I've seen before include "Furthermore" , "As well as" , "Positive and not a negative" , "asset" , "credit" .)