Since 2005 there have been between 150 & 200,000 Cobras, GT350, GT500 etc built by Ford and Shelby American. In the time between 1962 and the end of 69 they only produced just over 13,000 (1,000 Cobras) cars total. The new ones will never be "collectible" at the level of the originals whose legacy they are using as the sales pitch. If you want to narrow it down even further in mid 67 Ford assumed the assets of Shelby American. The tail end of 67 (thought to be the Z marked serial number tags) and all 68-70 Shelbys were built by Ford Motor Company not Shelby American. The 2005 GT500 was completely developed and finished by SVT before marketing struck on the genius idea to stick GT500 on it - they had owned the rights to the name since 1967.
So will they be an appreciating asset - nope - no way - never in your lifetime. Why? No history and not rare the things that drive the classic car market. Maybe in 50 years a nice low mileage survivor will sell for decent money so get one for your great grandson.