While you bring up some good points, there's ont thing that limits the effectiveness of the RB supercharger, scale. The squirel cage fans in furnaces have two things that work for them, size and number of blades. The bigger the diameter, and the larger the number of blades, the better the fan. Once you scale that down (and remember, air doesn't scale) to the size of the RB, the fan becomes less and less effective. Superchargers on 1:1 cars have lobe air pumps, not fans. Turbos have fans, but operate at crazy rpms to achieve pressure.
Now lets look at the air filter. From what I've seen and tried to figure out, the filter on the RB looks like a piece of coffee filter paper. There was no motor saver filter on any of the engines in the pix I have seen. This is pretty weak IMO.
Then there's the issue of keeping the engine tuned at all throttle settings. Assuming that the fan does produce pressure when it's spooled up, that would change the ammount of air entering the carb, but the needles are designed for non blown operation, and the higher the RPM the more air is blown into the carb. Seems like to me it would lean out the top end at WOT. Tuning for WOT would then richen up the low end, but the midrange on most engines can't be tuned.
I'm not saying that it won't work, but the headaches for trying to get it to work are more numerous than the benifit of maybe a little power boost. Plus it adds weight and drag to the engine.
On the subject of NOS and CO2 injection. there was one guy here that tried butane, and said it was worthless. NOS and CO2 are probably the same way. Tuning issues.