What could be ever so true -- art being seen as a valuable collection (8-5)
I believe the answer is:
treasure trove
'a valuable collection' is the definition.
(collection of valuable items)
'what could be ever so true art' is the wordplay.
'what could be' indicates anagramming the letters.
'ever'+'so'+'true'+'art'='eversotrueart'
'eversotrueart' is an anagram of 'TREASURE-TROVE'.
'being seen as' is the link.
(Other definitions for treasure trove that I've seen before include "asset to the government" , "Discovered valuables" , "lot of valuable things" , "valuable discovery" , "Hidden delights" .)