It's 50 year old technology, of course it won't keep up with today's products. Hell, look how far cars have come in the past 20 years.. Your argument is ridiculous. People buy them for the styling, the exclusivity, and because it reminds them of their childhood. Just like you will likely want your precious Subaru in 30 years when dealing with your midlife crisis, despite it being slow and poor handling by whatever is out at that point.
And, a basic resto-mod, redoing simply the rear suspension, with modern tires, will generally be in the 13-14 range.