Couldn't sound much more like a Doctor Who episode title, could it? They're notorious, especially in the earlier seasons, for the formula of "The (Blank) of (Blank)." And both "horror" and "void" would totally fit. I'm surprised they haven't used it (although there was an adventure in the Colin Baker days called "Terror of the Vervoids").
But no, this is a phrase I come across in religious contexts. First, I believe, in that marvelous little book of photos of Mexican churches, Divine Excess: The Mexican Ultra-Baroque. Mmm, mmm, mmm. One of my "all-time faves" on my LibraryThing account. Then yesterday, it was mentioned as a reason why Sufi calligraphers had an interest in the Egyptian hieroglyphics, because their aesthetic was similarly informed by "the horror of the void." (In Egyptology: The Missing Millennium, by Okasha El Daly).
A quick online search of the phrase brings up the decorative arts of Morocco, and the monuments of Angkor (I checked out a documentary from the library about the latter, and I should watch it, but I kind of lost interest when I discovered it was narrated by Sharon Stone. Yes, I'm that shallow!)
And then of course there's Aristotle's Physics, and medieval writers elaborating on the concept of how "nature abhors a vacuum." Even though the words "abhor" and "horror" obviously have a commonality, I don't think of them in similar terms. The connotation has always been to me more like nature disdaining a vacuum...and there I go with the personification again.
But this is all relative. A crazy over-abundance might be motivated by a sort of existential fear, a la "horror of the void," but mightn't it also be motivated by -- for want of a better word -- love, for the physical creation? That is, why leave spaces empty, when there's all sorts of extra cool stuff you could throw in there?
Especially since a lot of the real "ultra-baroque," crammed-to-the-brim art comes out of desert environments, where people face the idea of the void all the time. When they have the chance to beautify, maybe they just go all out.
Of course, I probably just think this way because my own house is stuffed full of stuff: I'm a maximalist. But until I see some hard evidence that Mexican architects and Muslim craftspeople are actually motivated by "horror," I can't accept that judgment on face value.
The phrase is still delightfully Whovian, and also rather Lovecraftian, though...