Why are you looking at the prices? Are you selling already? If not, why look?
You seem to suggest in your OP that the only reason you bought the Edition 30 is due to your believe that it is less susceptible to depreciation than other cars. I could be wrong but I like most peeps on here bought my car based on what it was, not what it would cost to run, insure or resale value in the future.
I Bought my ED30 5 months ago for just under 12k, no idea what it's worth now and (without being flippant) am not too concerned. I bought the "exact" car I wanted, in the colour I wanted, with the spec' I wanted (nearly) with the full knowledge that one day when I trade it in, it will be worth less, a lot less.
If your buying a slightly more specialised car such as an ED30/Pirelli or R32 there will surely only be a finite amount of people (enthusiasts) who will be in the market for them, or even know what they are. As the mk6 GTI and mk6 R become more affordable to us poorer Golf lovers I'm sure prices will go down quicker on the mk5.