I will say that: my N900 has had worse scratches, having never had worn a screen protector. Fortunately, it has no white spots, or any other problems with the display.
Broken USB... Find a soldering expert, and you can do anything, up to inductive charging.
SIM card error... Never used a SIM card.
Nearly broken screen which will work no longer than year is troublesome, indeed. Most applications are not usable in blind mode, as I had recently discovered. However, with gradual transition, it might be possible to reprogram the device to be at least phone-level functional - microphone and speakers, LED and buttons and keyboard are still here. Blind-shoot camera isn't comfortable, but it might get the work done. Besides, it is possible to connect TV as external display to N900.
It might be my phobia of screws that makes me protest the idea of separating N900 into parts.
I am not looking for an N900; merely attempting to cheer up others by describing how the device could be kept alive despite the injuries
Per aspera ad astra...