is a lot of the rendering in Spire much less clear and detailed than Tomahna and Haven?

I know it's darker, but even some of the glowing crystalline areas, such as the one you climb up through from the plant garden to find the console with four crystals in it, look like only a rough idea.

It depends on your definition of "less clear and detailed" but I will say: It's you.

The things that are supposedly man-made - that is that I assume Sirrus produced somehow - are nicely detailed. But look at the glowing area you can't get to beyond his lab desk. Or, as I mentioned, the crystalline area where you climb up the ladder through glowing crystal. Even the rock that you are close to looks to me like a novice roughed out an area that the more highly skilled artists were planning to come back to.