1720 Halfpenny

Nice coin John, I wouldnt be too worried about the verdigris, its there and there isn't much you can do about it, but If it was mine I would soak it in Olive oil for a few weeks, giving it a wee rub with a soft brush every few days around the verdigris area, I use an old toothbrush. Results vary, but what have you to loose, verdigris aside I would give it a grade of almost fine.
As for Value.........well like all coins, its only worth what someone wants to pay for it.