Yes, although...

: Our visual acuity can pick out much finer details in
: contrasty areas

That's something that "Snellen Chart" sorts of measurements for visual acuity already try to take into account, hence why Snellen Charts themselves have black symbols on a white background, and are sometimes even backlit.

: as well as pick out fine details in motion.

Err, strictly speaking, our eyes should tend to be even less spatially sensitive in motion.

It's fairly obvious that our brains can accumulate information as they view a moving scene. Similarly, they can interpret motion blur as motion vectors to better understand what's being looked at. Similarly but not directly related, vernier acuity is thought to be a result of the brain's interpretation of coverage, as opposed to an ability of our eyes to directly distinguish certain sorts of details. That stuff is all fine and dandy, but it doesn't call for a higher-resolution display.

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I don't really want to defend the charts that get thrown about the internet, because they're usually full of shit (the most common one, which hilariously uses 20:20 visual acuity as its baseline, is particularly awful), but there are extremely heavy diminishing returns on visual clarity past a certain point, and that point isn't really that far out. There's a reason I used a fairly aggressive comparison like "32-inch display at 10 feet" (which puts the width of a pixel at just over half of what's needed to display what you might call the "Snellen chart limit" for a person with average vision); I would be quite impressed by someone who could easily distinguish 900p versus 1080p in terms of raw visual clarity (i.e. comparing a 1080p image a 900p image, both downsampled from the same source image) under that circumstance. Or would you argue that my describtion of "rather subtle" is inaccurate?

Content being rendered at the two different resolutions would be another matter altogether, and in many cases it would be blatantly obvious, but that's not the question.

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: I would say this is true all other things being equal

Well, the question being asked was how noticeable the difference was, hence that assumption. You could spend forever debating what compromises are best for a particular product.