Acquires finally valuable area for expansion purposes (5)
I believe the answer is:
earns
'acquires' is the definition.
(earning is a kind of acquiring)
'finally valuable area for expansion purposes' is the wordplay.
'finally' says to take the final letters.
The last letters of 'valuable area for expansion purposes' are 'EARNS'.
(Other definitions for earns that I've seen before include "Merits through work" , "Makes - deserves (by one's efforts)" , "Gains by work" , "ready for work?" , "Gains by labour" .)