Many REALLY knowledgeable responses will be along any minute but for what it's worth the slightly amended body shape due 2017 is getting some negative views - too much unnecessary bling & discordant bodywork changes, albeit tiny.
Good luck with a discount on a new 55, the only deals I have spotted are on diesel SLK 's which are cluttering up a lot of forecourts. Current 55's don't have the soundtrack of older models. As always the best deals are on ex-demo's or 12/18 month old cars - depreciation always been the great enemy of SLK's.