Anything Matchbox + Coke + VW + somewhat limited production WILL go up in value.  Collector's price guides are not all that reliable to judge value . . . they may say it's worth $50, but if no one will pay that for it, it's not really worth it.  The best way to see what it's really worth is to see what they are bringing on eBay.  That will give you a true picture of its market value.