yes you are right, the RNS 510 still treats the iphone as a 'CD player' and just displays track number, no other info. Im pretty sure MDI solves this, but its £250. waste of money.
Im not 100%, but I dont think the dock connector will even charge your iphone, as original ipods and mk1 iphones used a different pin for charging and VW never updated it when apple changed the pin in the dock connector in 2008, as far as im aware.