In the reading I've done since posting my argument that ornament is for enhancing memorability, I still haven't found anyone who's noticed the connection to memory. Some arguments were variants of the lazy economic interpretation about ornament being one weapon used in the struggles between and within classes, obviously wrong since it shows up too much in primitive societies where it's used only to distinguish ethnic groups at war with each other, not as weapons themselves in inter-group conflict. Plus ornament, where it's practiced, begins too early in life -- little girls trying on lipstick and little boys getting temporary tattoos are not part of any class conflict.
The mainstream view, though, was more about ornament as giving pleasure to the audience. Functionally the thing could exist without ornament, but adding it on top makes it so much more pleasing. And when certain movements want to strip surfaces of ornament, it's because of some Puritanical drive against the indulgence in pleasure, seen as sinful, decadent, corrupting, etc.
I don't deny that pleasure plays a role, but it works at a later level than what is ornament for, which is memorability. Some ornaments are more memorable than others, and some of that variation could be explained by differences in how pleasurable they are. Still, if anything pleasure is a means to the end of memorability.
How about a quick test, though? If we consume ornamentation for pleasure, then there should be something analogous to sensory overload and a de-toxing period afterward. Consider clear cases of pleasure like delicious food or no-strings sex. There is such a thing as too much delicious food and too much sex. If pushed beyond that limit, we experience an overload of the organs and senses involved in the pleasurable activity. Soon we go into a refractory period where we can't get eat any more ice cream or go for another roll in the hay, even if we wanted to (which we don't).
We feel nothing like that when we're confronted with excessive levels of ornamentation. We feel puzzled about what exactly it is we're looking at -- there is just too much detail to clearly make out what is underneath it all, at a specific level. We may know that it's a building underneath all the high-relief sculpture, or that there's a melody somewhere under all the warbling, but we don't get a feel for the unique building in front of us or the unique melody we're hearing.
Excessive ornamentation is therefore an overload of the learning and memory systems -- we can't learn what specific thing it is that we're looking at, and so cannot store or retrieve it from long-term memory. We turn away feeling un-satisfied -- we wanted something memorable! We do not nearly collapse from our senses being over-satisfied.
What about those recurring movements that want to abolish ornament? Again I think there is some kind of revulsion they have toward pleasure per se, but that isn't the main motivation. They mostly want for buildings, melodies, etc., to be forgettable. Of course they still want them to be remembered -- not because of any memorable features, but because you're just supposed to worship this building and that melody. The arbiters of architectural and musical taste said so. It is always the mark of a low point in culture when the mainstream insists that we remember forgettable things.
This view explains the authoritarianism of such movements, which is hard to account for if they were merely against pleasure. Edit: Perhaps the anti-pleasure view can capture this too, like if people need authorities to steer them away from their inborn inclination toward pleasurable things.
It also goes with the heavily socially avoidant personalities that these people have -- let me be in my cell in the hive, and I'll let you be in yours. Avoidant people need attention and esteem like everyone else, but they don't want to connect with others, so that only leaves attention-whoring. Look at me and tell me how awesome I am, but not because I've reached out to you and done something worth praising.
On the other end of the spectrum, truly ornamental movements have no leaders, issue no manifestos, and have no desire to force their policies on the masses. Being more socially out-reaching, they lack the pretentiousness and self-consciousness that would kill the mood of belonging to a wild crowd atmosphere. They want to be remembered only for having made something memorable.
This shows why the Victorian pro-ornamental school never achieved the greatness of the earlier Romantic-Gothic period (i.e. Regency in England and Empire in France), the Art Nouveau and Art Deco periods not too long after, or the New Wave look of the 1970s and '80s (I mean the whole visual culture, including movies by that point). They may have genuinely wanted a return of a healthy level of ornament -- neither bare nor bewildering -- but the zeitgeist was too far in the authoritarian, avoidant, manifesto-writing direction. That hyper-activated sense of self-awareness kills any chance you have of falling into the dream state and letting the ideas, words, and pictures just flow out.