Best way to decide, would be to try both of them out, and see which one fits you best. Ideally, one right after another, and in the exact same places.
A hard run up and down San Bruno Mountain would be a pretty good place....

I'd tend towards the 500E, as it's a collector's car, already, and it's virtues are well known. In your case, with your experience with your '87 diesel, you know the basic body style really well, which is a big plus in taking care of them.

But the E55 AMG would be a delightful car for road trip cruises, no question, and would be a real sleeper at the drag strip, too. Not to mention it's safety features are more advanced.

But it does have complex electronic issues, and I think it might prove to lack the build quality and durability that you would get with the W124 E500.

Verdict seems to be in already, on resale value. The E500/500E is already the winner on that one.

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)