What is so hard about a GUI for at least the basics?
I wouldn't oppose that, so long as that not the only option. Some of these we already know, but in my opinion the best things they could possibly do to keep ciV as the most moddable series ever:
1) Use the same code from civ4 (XML, C++), hopefully python will be there also.
2) Provide a GUI for editing XML.. nothing special here, just make it easy to change attributes for novices.
3) Release at least as much source code if not more than they did for civ4.
4) Keep the Gambryo graphics so we can still edit in blender and nifskope for free
5) provide an external model/skin editor similar to the one in Spore. This would be the biggest boon to scenario mods and the like.
6) keep using dds textures. not sure what other options there even are, but this is easy enough.
7) maybe the most important, provide a world builder that actually works, and with more options and functions than before
that way for example you could do XML by hand as we all love to do, or you could use a GUI if you are doing simple changes. At least allow us to still use blender, but if not provide something better and more powerful. Seriously its looks like a small graphics change relatively from civ4 to civ5, so why complicate things?
back to the religions/espionage discussion.
If I were to really break it down I would say more like the espionage was an afterthought/poorly implemented. Spies are nearly pointless, commerce is much better spent on research than espionage, the benefits of high espionage is negligible. Until you can build jails, intelligence agency's ect. its a choice between the commerce types. I'd say most people go full throttle research, that is if you are trying to win.
Religion in civ4 was not bad, but just too static of a feel. I guess its supposed to be that way. Maybe all it was missing was more religious events or something like that. I could totally understand why they would remove religion though, its just too complex to truly model it accurately. We always end up with buddist napoleon or some other lame.