A B767-300ER flight crew dealt with a variety of recalcitrant system anomalies related to one degree or another with low right pneumatic system duct pressure.

Narrative

On descent; right engine anti-ice valve discrete light illuminated. Right [pneumatic] duct pressure indicated 10 PSI; left duct pressure indicated 28 PSI. Increased right engine N2 until pressure rose and right engine A/I [Anti-Ice] valve extinguished. Flaps and gear were needed to add drag so as to comply with ATC 180 KTS restriction. On landing; the First Officer announced 'no spoilers.' I manually deployed spoilers; and then tried to reverse the engines. The right thrust reverser would only go to idle detent; but would not move beyond and accelerate the right engine. I released pressure and tried to bring the lever up above the idle detent 2-3 times. I finally; reversed the left engine slightly while braking and holding right rudder. After taxiing off the runway; the First Officer stated; we had an auto-speedbrake EICAS annunciation on landing; it was now gone. However; 'idle disagree' was annunciated as well as an amber REV annunciation; with the reverse levers stowed. I cycled the right reverse lever two times and the amber REV disappeared; as did the 'idle disagree' message.This was a non-event because; these malfunctions occurred on a VFR night; landing on a 13;000 FT dry runway. Had these malfunctions occurred in IFR conditions while landing on a short; contaminated runway the airplane could easily have overrun the pavement. The multiple malfunctions; occurring during a critical phase of flight: landing roll out; should be investigated so as to prevent an accident in the future.