Just a couple questions and/or suggestions:
1-- Is there any particular reason why you chose twinview rather than Xinerama?
2-- It's easier (& I believe more preferable) if you could post the file, rather than attaching it. If you were to post it though, it would make it easier to look at, if you removed all those comments in there, and just post the important parts (the uncommented stuff). They really put a lot of extra crap in the default file don't they?
3-- I've always been able to span wallpaper across both screens, in KDE, using Xinerama, which is why I asked about that. I'm not 100% sure if you can do that with twinview (or not). Xinerama IMO would be worth a try though.
4-- Does KDE offer you the option to span it across both? Or is it simply not an option at all? (I have spent very little time with the new KDE as yet)