Hey Dave,
I'm 49 and recently bought an 03 Azure Blue Mach 1. Depending on where you live, you may be able to find a super deal on a leftover 03 Mach (22k-23k with rebate). I went with the auto, simply because I'm just not into all the shifting anymore. The 5 spd is a little faster, has a forged steel crankshaft, and tops out a little faster. The Mach does require premium gas. I've had my auto to 148mph, which is plenty fast for this old man. The comfortweave seats are very comfortable and the design of the Mach 1 is as impressive as its performance. A downer is that insurance may be a little higher, depending on your record.
Both the GT and the Mach will get you from point A to Point B, the Mach will get you there with a much bigger grin on your face, and its really fun to watch the young pups drool when they see "gramps" drive by in their dream car... A singular plus for the GT is that its cheaper.
One last point, the Mach will probably hold more of its value against the much hyped 05 Mustang, due to it being a limited production, high performance model.
Check out
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for alot of great information about the Mach 1 and ask other owners what they think. Many owners are our age. I don't believe you will find a single member that regrets their purchase.
I hope this helps!