Welcome to Stangnet Havoc 2.
Magic 8-ball says the future is "uncertain."
Buying a car as an investment?
Usually not the best option to invest money in.
Hard to say what an 03 or 04 will bring in the future - are you looking at selling it 10 years down the road or something? 20 years? 35? Late model cobras aren't exactly "investment" vehicles like the older muscle car era 'stangs of the 60s (ie - $100,000 cars).
Even if you bought a new 10th Ann '03 Cobra when it was released to the public, put it in a plastic bubble wrap (some folks do such things LOL), and tucked it away in a climate controlled storage facility, it's going to be quite some time before anyone will really know how much money the car will bring at say, an auction.
Have the 03s and 04s retained a decent amount of their value over the past few years? Yes, because of their demand, potential to mod the car and make gobs of horsepower, etc - it's what every Mustang enthusiast wants out of the box, especially for those who take their car to the drag strip.
My advice would be to buy the best 03 or 04 you can and drive it now so you get to enjoy it. Be sure to check out the Terminator FAQ in our "SVT Tech" section, linked below:
http://www.stangnet.com/mustang-forums/681843-03-04-cobra-faq.html
G'luck.