yes, i will be buying a GND to achieve better results for achitectures.
So i think i bought the CPL for nothing? only good is to reduce reflection only
while a GND can be very useful, another possibility is to shoot when the contrast is not so great. eg, early morning, late evening. strong side light, front lit building will give u well lit building w deep blue sky.
also, buildings stands like sticks on the horizon, so, while using a GND to darken the sky, one risk darkening the buildings as well. so, in this case, a polarizer is still useful as the polarising effect darkens the sky.
*my understanding is that from a basic meter reading, adding a -2 EV strength GND over the horizon will "under-expose" the sky by 2 stops, thus preventing it from getting "over-exposed" (the sky is ususally much brighter than the land), thereby preserving the details in the clouds (cus the clouds are finally correctly exposed).
*the polariser will darken blue sky, giving more contrast and distinction between the edge of the cloud and the sky, giving a more pronunced effect. details in the cloud may still be blown out, cus, both the land and the sky gets the same exposure even though they are of different brightness.
and if u ve both filters, i think its possible to combine them. ve read that many landscape photographers do this, though, personally, i ve little experience w filters.