Pop up to extol value (8)
I believe the answer is:
appraise
'value' is the definition.
('appraise' can be a synonym of 'value')
'pop up to extol' is the wordplay.
'pop' becomes 'pa' (both can mean father).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'to extol' becomes 'praise' (I've seen this before).
'pa' in reverse letter order is 'ap'.
'ap'+'praise'='APPRAISE'
(Other definitions for appraise that I've seen before include "Judge" , "Consider comprehensively" , "Assess or evaluate" , "Assess the value/quality of (something)" , "Estimate or assess the value of" .)