It really does seem like a very bad idea. Then again, people of the prior generation would seek out a 1968 Camaro or a 1963 Corvette Stingray, which could be, and often were, equipped with terrifyingly large engines. A Camaro or Mustang or other muscle car from the 60s, in particular, are kinda famous for being able to go really fast, but only in a straight line.
So, yeah, I just can't see it. Even if I had that kind of disposable income, and even though I have on a couple of occasions considered buying a Delorean (when I was in my 20s I even looked at one, but it needed more work than I was willing to put into it), the factors that led to it being under consideration just don't line up with a new one at $100,000. The one I was looking at was listed at $10k, and I think the seller was hinting that he'd take as little as $7k by the time I walked away. In short: As a project that didn't cost a fortune and didn't need to be a daily driver, it seemed like maybe a good idea.
Especially with the purported engine upgrade. A 400 HP modern engine in something that might have struggled to meet early eighties standards of braking, handling, and so on is a shiny coffin.