I know someone who uses a heat gun which will dull the coin, as always if you're going to do that then practice on a valueless coin first. I've not got any first hand experience of that but I've seen the results and it's definitely an improvement. That coin you've posted isn't too bad already though.
Very rare because it's unresearched... http://www.ebay.co.uk/itm/UNRESEARCHED-HAMMERED-PENNY-VERY-NICE-CONDITION-VERY-NICE-RARE-COIN-/252120779344?hash=item3ab391ca50:g:DpoAAOSwl9BWGjnj