Excuse my title gore.
I've been modeling Gothic architecture:
Here's the blend file I've been practicing with.
So I'm extruding along curves a lot. The complication is the fact that just one curve with a highly detailed bevel object won't work. You'll often need part of your beveling to split off into additional tracery, or to omit it in certain places. So you'll need a bunch of similar curves with different bevel objects.
I end up with a bunch of meshes running perfectly parallel to each other, which prevents the use of the Boolean modifier, the obvious answer to this question, even after dealing with n-gons. I also have lots of hidden faces from tucking curves inside each other to hide my end points. Cleanup and decimation are often necessary to prevent Blender from hanging when you tab into edit mode, actually.
What I'm asking is how I can reduce/eliminate internal geometry, ways to reduce my face count (especially parallel faces), or any other advice you might have relevant to the end of modeling Gothic architecture. I'm probably doing something wrong or inefficiently.