Cleaning may make it more effective, but generally, if the butterfly valve isn't moving the car saw 200,000+ miles, all driven by a granny, all in 3rd gear, while cruising at less than 30MPH (Yes, Sparky, we're referring to your car here :icon_razz ) or something else broke first. Moving parts become impaired as debris builds, but they don't stop moving from it... at least not from this kind of debris, now rocks... you got rocks blocking it, then, then you've got a problem (and probably a mad neighbor who would like to know where his prized rock collection keeps going late at night).
I'm not saying not to clean it out... not by a long shot. Mine was filthy and so was SupraRX7Nutter's. It's definitely worth cleaning out, but if that's all there is that's keeping it from moving then you've got something else to look for (see: cracked diaphragm and cracked vacuum hoses) as it should have a lot more pressure moving it.