Art as trendy, every other piece highly valued (5)
I believe the answer is:
Here is my best explanation:
'highly valued' is the definition.
(I've seen this before)
'art as trendy every other piece' is the subsidiary indication.
'every other piece' indicates alternate letters.
The alternating letters of 'artastrendy' are 'rated'.
(Other definitions for rated that I've seen before include "Assessed; merited", "Graded by trade", "Adjudged", "Scolded, estimated", "Had a high opinion of", "Stormed", "Considered", "Trade (anag.)", "Reckoned" and "Assessed, valued".)