Crossword Genius

Sponsorship: something valuable with added interest (7)

Ross

I believe the answer is:

auspice

'sponsorship' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for auspice that I've seen before include "future promise" , "Omen; epic USA (anag.)" , "Portent" , "Omen - I use cap (anag)" , "Omen (archaic)" .)

I've seen this clue in The Times.
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