I saw that E9 convertible in person.
It is at the Technik Museum in Speyer, Germany. When I was visiting there, I just stood there and thought..... WTF!!!!
I had the same thought about 'how can that thing stay together' - without having a literal ton of body reinforcement installed. LOL
And on the other shoe (following along in the mode of this thread) - I have had a 68 Mustang Convertible GT since 1979.
Drove that same car when I was in high school and stayed in the family since then. I took it to Seattle in 2004 or so after my father passed away. I had it TOTALLY restored in 2006 and drives great, so to speak.
But, that being said - it does not compare at all to the 2002 or E9 in how it feels on the road.
Even after it was restored (with all new suspension and such) - I call the steering wheel in the Mustang a 'suggestion device'.
After I had the Mustang restored, it did behave on the road much better than it did before, but...
1960's Detroit engineering (no matter in how good a condition) does not compare at all to how my (not restored) 2002 and (at that time not restored) 2800CS drove.
Not even close.
But - the Mustang is absolutely excellent at cruising along the (smooth) roads in a leisurely manner. Sounds like that may be more of what you are looking for now...
Depending on what you want to do - can't go wrong with either angle - Good luck in your search