Quite possibly the two largest things between the two for me is I think of the 87 as just another car, my 84 gets quite the notice whether good or bad, the 87 also seems like it'd be much more of a highway vehicle while my 84 loves going 45 but hates 75 (mileage wise).
I'm itching for an 87 even more now than ever.... I really just want something I'll keep for a LONG time, something I can safely sink some money in and get a good return in service. It seems like whatever I put into the 84 won't come out in resale, so why bother? Or just as edge just posted 'you can replace everything but miles.' Everything I want to change designwise on the 84 is pretty much like how the 87 was designed.
Why pay $4k if they settled at $3.5k?