Straight headland's simple elegance (8)
I believe the answer is:
neatness
'simple elegance' is the definition.
(I've seen this before)
'straight headland's' is the wordplay.
'straight' becomes 'neat' (synonyms).
'headland' becomes 'ness' (both can mean a promontory).
'neat'+'ness'='NEATNESS'
(Other definitions for neatness that I've seen before include "Orderliness" , "well-tended condition" , "smart condition" , "Tidy quality" , "Well ordered" .)