The bad-plastic-around the bumpers is a problem I've seen on Cordobas/Miradi, but never Imperials. Probably a different vendor/material.
In the late 70s/early 80s, everyone was doing "retro" 1930s luxury touches. Giant whitewalls, upright grilles, fender vents, two-tones, padded tops and yes, bustleback trunks. (Lincoln also did them on the '82 Continental Sedan.)
Personally I think the Imperial did the best job on the trunk (which also gave it useful space, unlike brands C & L). I also like the mix of both retro and "futuristic" styling cues (the narrow full width tail lamps, minimal ornamentation, near-flush glass, molded fascias + digital dash and EFI as functional items)
I have a lot of internal memos regarding the planning of this car. I recall customer clinics really thought the Mark VI styling was terrible when compared to Imperial. The decklid fit was given extra labor time to assure it would close with a finger tip touch, vs. the additional cost of an electric pulldown. Imperial body panels were thicker steel, this was done after a cost/benefit study of typical panel damage done in material handling vs. new dunnage to prevent damage. It's interesting stuff, lol.