After a long, long time since I started digging this question, I finally found a way to rip Devil May Cry 4 textures from the game itself. (Big thanks to User:BTHR Zero X who showed me that it is possible.) I bet it isn't the best way to do it, but I haven't found a better one... at least, yet.
For the record, I use 3D Ripper DX to rip the textures from the game and create a dump of DDS (Direct Draw Surface) files. Then I use GIMP with a dds plugin to view and save them as PNG. The dumps are pretty big, but it is worth it.
Also, as a support tool I use Windows Texture Viewer. It is incredibly convenient for viewing, since it is fast and seems to be highly compatible (for some reason I have some troubles with GIMP plugin), but, well, it can only view files, not save them.
In other piece of news, 3d Ripper DX is, as I understood it, a multi-purpose tool that can rip graphical stuff from DirectX games. So maybe, just maybe I can use it to rip files from the other games... Yes, including the first two, since the emulator I use uses DirectX to draw stuff... I think... I'll try to do it sometime.
Feel free to add any suggestions. I'm a newbie in all this, trying to get source files and such, so I'd really appreciate it. Also, feel free to put a request for something - I'll try to find it.
Current list of ripped files that I uploaded to the wiki: