Just to add my two pence to this....I have owned a 25th Anniversary and now a proud owner of an Edition 30. I love the way they look, they are both head turners and yes I did pay the premium for both...purely because like any other was after a mint condition motor and the whole exclusive thing about it. Now...they do depreciate but not like a standard GTi by far. I owned my anniversary for 5 years and lost near enough 1k on depreciation on it a year. I paid 10.5k 5 years ago for a 5 year old car. Considering it was heavily modified diesel (hybrid turbo, miltek etc etc) and over 121k on the clock by the time I was done I sold it within 3 days of putting it up for sale! Putting aside the mods, a 1k drop a year isn't too bad.
Baring that in mind, an Edition 30 is about 4-5 Years old now and going for similar prices as the Anni 5 years ago, so hopefully the trend stays the same going forward. I guess the only argument is that the Edition 30 is a petrol and generally Diesels tend to hold their value a bit. Time will tell I guess!