The most common and most likely answer to this crossword clue is the 9 letter word OVERVALUE
I've seen this crossword clue in The Times
O
V
E
R
V
A
L
U
E
More clues leading to the result OVERVALUE
Buddy explains!
The straight part
We know that "Set too much store by" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case set too much store by = overvalue.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.
What does OVERVALUE mean?
OVERVALUE verb- To assign an excessive value to something.