They're stupid enough to make a valuation pointless at the end (5)
I believe the answer is:
asses
'they're stupid enough to' is the definition.
The definition suggests an adverb but the answer is not.
'a valuation pointless at the end' is the wordplay.
'valuation' becomes 'sse' (I can't justify this - if you can you should give a lot more credence to this answer).
'at the end' says to take the final letters.
The final letter of 'pointless' is 's'.
'a'+'sse'+'s'='ASSES'
'make' is the link.
Can you help me to learn more?
(Other definitions for asses that I've seen before include "Pompous fools" , "Animals of horse family" , "Small, sure-footed animals" , "not the most sensible types" , "Jennets" .)