I had a faulty SR300 for months that began working perfectly again. After going through everything I'd done today that might have changed its condition, I found the answer, and confirmed that it was what was making the camera work (as it would only stream when this solution was active).
Here's the tech details:
* Acer Aspire Es 15 laptop with USB 3.0
* An unpowered USB 2.0 4-port hub
* An Android tablet
* A Micro USB tablet charging cable
* RealSense SR300 camera plugged into the USB port on the back of the laptop (not the hub)
With the SR300 plugged into the USB port on the back of the PC, I connected the Android tablet to the USB 2.0 unpowered hub via the Micro USB cable with the tablet switched off, so that it entered battery charging mode.
For the duration that the tablet is in charging mode, the SR300 camera is fully functional in every way. As soon as the tablet is disconnected from the USB 2.0 hub and its charging ceases, the SR300 stops working.
If people having problems with their SR300 also are fortunate enough to own a tablet (or some other USB chargeable device), I recommend giving the above process a try. There's nothing to lose!
Edit: the process seems to require that the device being charged has less than 100% charge on it. If the device does not allow the charging process to proceed because the battery is full then the SR300 camera signal cuts out.
Edit 2: 24 hours after the initial posting of this article, the SR300 camera is still functioning exactly according to the rules above, and the point about connected devices needing to have less than 100% charge in order for the camera to work normally is verified.