I finally got around to trying this properly with a lot of models from model resource folder I have.
Firstly, Kizoky's GLDEF generator was a godsend. I just dropped the models folder onto the exe and it spat out a flawless GLDEFS for every graphic in the folder - including sub folders - with correct paths and everything. Almost 800 models skins allocated to the SimSun shader in less than a second.
Then "all" I had to do was browse through my models folder to try and identify the skins that I didn't think would work too well with this. This turned out mostly to be skins for models that are meant to be light sources. The shader darkens them and the problem is particularly obvious for ceiling lights where the underside gets darkened the most.
Fortunately, it was an easy job to go through the folder to identify these and a few others. The skins that I deemed unsuitable for shading were very much in the minority and visually pretty obvious when scanning through the thumbnails by eye.
There were, also, one or two model skins where I was already using another shader on them and these can't co exist so I had to decide wither to keep the original shader or go with SimSun. Again, this selection process was pretty easy because there were only a handful of these and, of course, they are all already listed in a GLDEFS file so it was easy to find them in that file, search for the same graphics in the SimSun generated file then decide which one to comment out.
I guess the whole process took about 20 minutes - so no big deal really for so many models.
And the end result is very nice. As others have said, it's subtle (which is good) but definitely there and when switching back and forth between using the shader and not, the unshaded models very quickly started to look quite flat in comparison.
I'll still have to go through the models and evaluate them more thoroughly in game where they are most likely to be used but as a big, brutal, bulk test of both the GLDEFS generator and the SimSun shader, everything worked very well and the whole thing was surprisingly painless and error free to set up.