Small, but crucial update - I think I've found solution for glitched triangles. It is not as good as it could be, but in my case it was the only way. It is very easy to fix in easygen (no more searching for glitches in radiant!).
First of all - all glitched triangles were FLAT. As I looked through my maps and experiments, it became obvious that all flat surfaces generated by easygen suffered from errors. If you want to leave some plain terrain for buildings etc., you should do it afterwards in radiant by merging triangles in that perticular area, or by adding extra brush covering/substracting glitched space. If you have a map which suffered from errors, and you still have it saved in your easygen (.egn files) directory, you can easily locate and change all flat surfaces by clicking button, which will highlight plain triangles. Then, you should use optional modifier - smooth, hill, whatever you want, just something which will tilt those triangles and remove red markings. Give it minimal value, so overall look of terrain won't change that much.
I'm still working on that texture problem, so any help would be appreciated.
Edit: Textures fixed. Don't ask how, it's too embarrasing for me. And I was right, it was something VERY obvious. Solved!
