Well, I decided I'd go against the system, load up my Photoshop CS6 and open up what I could find and do my best to upscale it to 1920x1080 while maintaining at least some level of the original quality. Believe me, that's a hard task to do when you resize something almost three times its original size.
Luckily, I managed to get some decent progress at least.
I stuck with only the event CG, as the sprites don't exactly make for Wallpaper material. There's scene CG from every main character; Emi, Rin, Hanako, Shizune and Lilly, as well as some wallpapers for Hisao, Kenji and Misha. A lot of these are groupshots, and luckily those were large enough to upscale without any major issue, where as those with only one character in them tended to be lower res and thus harder to work with.
(I realize there's a bias towards Hanako in this but YOU WILL ALL HAVE TO DEAL WITH IT.)
They're all PG. I didn't work with any of the sex scenes under the train of thought that it's unusual for people to want nudity as their desktop wallpaper. Feel free to object!
Of course, given that they ARE after all upscaled, there will be quality loss. But hopefully I managed to remove too much of the upscaling damage. Don't worry, though, they're all the same aspect ratio, and cropped to fit the widescreen.
Here's the link; I hope you enjoy them!

If you have any requests, send me a PM. Although, I cannot guarantee that it will look good.
Some more outside of the pack not made by me!
pandaphil's wallpapers!
http://fc08.deviantart.net/fs70/f/2013/ ... 5sfjzc.jpg
http://fc05.deviantart.net/fs70/f/2013/ ... 5sfbug.jpg
http://img163.imageshack.us/img163/7323/hanakowall2.jpg