Yes, whether things would look too out-of-place would be my concern, as well. I think that, as with any modern Q1 extension, use of 32-bit textures would need to be judicious.
There's some evidence that suggests to me that 32-bit textures are acceptable in some contexts:
* Players don't seem to complain about all of the maps that use 32-bit skyboxes, and many maps rely on those colourful skyboxes for visual effect. On the other hand, the skybox isn't part of the level geometry, so maybe that's why it doesn't bother people?
* One map which has always stuck in my mind for using external textures well is Necros' ne_marb
. It uses external textures to transplant Doom's green marble textures into Quake. It's been a long time since I've played it, but my recollection is that the difference between playing with the external textures or without was striking. (N.b. this was one of the first Quoth maps, and IIRC the external textures were included with Quoth itself, not in ne_marb.zip).
But, neither of these are exactly the same case as the artworks in these maps. So, I don't have much of a point, just thinking out loud!