Plain dish has value every now and then (7)
I believe the answer is:
plateau
'plain' is the definition.
(I've seen this before)
'dish has value every now and then' is the wordplay.
'dish' becomes 'plate' (plate is a kind of dish).
'has' is a charade indicator (letters next to each other).
'every now and then' means one should take alternating letters (letters selected at regular intervals).
The alternating letters of 'value' are 'au'.
'plate'+'au'='PLATEAU'
(Other definitions for plateau that I've seen before include "Raised level area" , "Large level tract of elevated land" , "level part of range" , "Area of flat, high ground" , "Table" .)