I cannot find another purpose for the Golden Symbol of Suon other than being useful in the Grimvale Quest - The Curse Spreads. I tried to do some testing like seeing if it cures anything, it didn't seem to. Of course, it makes a great decorative piece and something to have handy in your backpack if you want to show off a cool animation. You can purchase this quest item from Black Bert for 10,000 gps. If the Golden Symbol of Suon had some sort of special attribute, I think it wouldn't be something Black Bert would easily sell to you especially for that low. According to the Genesis, Suon is the son of Fardos and Fire however is calm and considerate. There's also a book about Suon:
"Suon, the Benevolent King. Suon is a kind and gracious god, a son of Fardos and also called the Life-Bringing Sun. Unlike his sister Fafnar he observes creation with love and blesses all creatures with warmth and growth. The worship of Suon and Bastesh grants Kilmaresh the stability and growth that the empire needs to prosper and flourish." Source: Suon (Book)