The most common and most likely answer to this crossword clue is the 9 plus 8 letter word LAYÂ GREAT STOREÂ BY
I've seen this crossword clue in The Guardian
L
A
Y
Â
G
R
E
A
T
S
T
O
R
E
Â
B
Y
Buddy explains!

The straight part
We know that "Value" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case value = lay great store by.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.