iirc the limited edition contained extras for use in-game like Dogtags, the SPECACT kit, some weapons and free access to Back To Karkand DLC, £90 sounds seem a bit too steep but being a physical copy I guess that probably warrants a higher price then original retail price. I wouldn't personally go above £40 for it but it's definitely slightly worth more than original retail considering it's packed with the DLC and the novelty of having a Limited Edition physical copy.
Edited:
Wait 10 years, then it might be a collectors item.
Edited:
Original World of Warcraft collectors edition sells for about $1000 now.
this works too