I am posting an answer, as I have somewhat managed to resolve the issue. I say somewhat because I still have problems.
Wheezy appears to have a need to use a screensaver. I disabled all options I could find, even patched xscreensaver, but to no avail. The above fixes I tried in my question, sometimes generate issues when I log in, some times they do not!
What however seems to have solved the issue is two things:
I stopped used VLC. I love it, used it for many years, but it is the culprit that spawns those xscreensaver sessions. I am now using dragon-player, and I can watch videos without the xscreensaver coming up.
I forced KDE to use a screen saver I chose. This appears to override the default xscreensaver sometimes.
Sometimes the screen goes blank on its own, without displaying the screensaver I chose. This is not my monitors (I use a dual setup so it would be weird for both to power-off). This appears to be at random, as sometimes the screen stays on for hours without powering off.
I even tried patching xscreensaver, but nothing worked. I hope this is fixed in the next stable Debian.