13 hours is a long compile.... I normally give up after 6.
If you want, I am happy to have a look at it. I had some success with VooDooPig's recently. Just zip the .rmf and .bsp and e-mail it to me.
On the func_wall debate, Yeah, there are two theories. SlayerA is right in that by making some of your brushes into func-walls, you will reduce the render split caused by that brush when it touches another brush. An entity brush placed on a normal brush tricks the engine into rendering the original (normal) brush as one rather than spliting it into two where a normal brush would join. However.... an entity brush that has a texture applied still has to be rendered, and unfortunatley does not block VIS. So the savings are minimal.
Compile times are not a huge worry (normally:-), wpoly count produced by the amount of textured brushes the engine is trying to render are, and these can only be truely shown after a full compile.
The long compiling times are normally caused by a large lightmap or complex brushes. A single log wall can take over an hour to compile by itself.
I am not sure that the engine renders entities as the player approaches or in the players view, I have never encounted any difference in Normal brushes vs entity brushes and the engine sees a lot more than the player does and compensates by trying to render things it thinks the player will see. In my experience the engine treats them the same. As for entity brush effect on compiling times, I doubt that they would speed it up, unless used to build the map in a better way, nor would they slow game play down.
If you want a better understanding of all this check out FireBinders Test Chamber at:
http://home.att.net/~firebinder/halflife/TestC_01.htm It is a working example of true results on r_speeds.