The T-Bird is not a good comparison because:
1. The market for 2 seat cars is very limited.
2. The whole car turned out to be below expectations because the original D/EW-98 unibody flexes too much with its top removed so they had to add a ton of bracing to try to strengthen it and its still not as stiff as it should be. How many of you know that the T-Bird weights more than a Lincoln LS?
3, Its $10K more expensive than a Mustang which further limits sales.
4. When it first came out many of the dealers just plain killed sales by trying to gouge customers with $5K to $10K markups.
5. As someone said, the original engine was underpowered. This was fixed for 2003, but the original reputation lives on.
6. MTX is not availble.
7. When the T-Bird went on sale the US economy was headed into a big recession.
8. The market for convertable cars is just plain limited.