Gone off old, mostly stupid style of architecture (9)

I believe the answer is:

neogothic

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'gone off old' is the definition.
The definition suggests an adjective which matches the answer.

'mostly stupid style of architecture' is the wordplay.
'mostly stupid' becomes 'neo' (I can't justify this - if you can you should believe this answer much more).
'style of architecture' becomes 'gothic' (Gothic is an example).
'neo'+'gothic'='NEOGOTHIC'

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I've seen this clue in The Daily Express.

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