Imaginative architectural feature in mind — millions expended (8)
I believe the answer is:
inspired
'imaginative' is the definition.
(thesaurus)
'architectural feature in mind millions expended' is the wordplay.
'architectural feature' becomes 'spire' (church spire).
'in' is an insertion indicator.
'millions' becomes 'm' (abbreviation).
'expended' suggests deleting specific letters.
'mind' with 'm' removed is 'ind'.
'spire' put into 'ind' is 'INSPIRED'.
(Other definitions for inspired that I've seen before include "Filled with (divine?) power" , "Brilliant (guess); aroused" , "Having a suddenly brilliant idea" , "brought about" , "Drew in" .)