I see no harm in providing the crew a few treats on arrival. I seriously doubt you''ll get upgraded, but maybe...graft works in mysterious ways.
I wouldn't count on a gate agent to do anything--that's a bit on the iffy side of policy in most cases. Certainly not to bypass anyone else' priority. I don't think the OP was suggesting that at all, flassher.
I would always look for the senior purser or team leader(DL) and offer a nice quantity of sharable chocolates, like Hershey miniatures--maybe a bag each front and aft?
At least you will be remembered for your thoughtfulness.