Was basing my theory off Miles Dagouter, who if I recall correctly, constantly tapped gold allomantically to further increase his feruchemical reserves (and later due to the body's addiction?). Second, unlike the leecher, effect of nicrosil misting is immidiate and uncontrolled (insta-boost like duraluminium) so it's also unlikely the reserve in you would get correctly compounded and converted to feruchemical charge if you were wearing some extra gold on you (since all the gold in your system gets wiped).
Thing with Nicrobursts is you don't expect them to be used offensively against the other side due to unforseen ramifications when they flare the enemy. But the grenade kinda offsets that by keeping the misting hidden/supporting his side when needed.
The boosted gold shadow was just an extra point. Your argument that nobody ever tries to flare A-gold is exactly the reason I'd look for odd behavior But that requires some canonized answers. Similar to how Elend using dura-atium was described as all-knowing chessmaster in one of WoB (I'm paraphrasing now), it could go pretty crazy with the gold.