In urban combat, accurate plunging fire on targets concealed behind the vertical walls of buildings only a couple of hundred meters from friendly troops is crucial.  For this, the U.S, Army depends entirely on the Predator drone, but it is expensive, unreliable in inclement weather and only carries two Hellfire missiles, enough for assassination missions but not for sustained combat.  The Nona is vulnerable to the Warthog, but it has gained this reputation in rural areas; in cities it can duck and dodge behind buildings and holds little fear of the Warthog, which dives at only 30° and typically cannot fire over the buildings on one side of a street to hit a vehicle driving on the opposite sidewalk.  Also, while the thin-skinned Shilka is no match for the Warthog in the open field, Warthogs have never been deployed over a city of multi-story buildings with hundreds of Shilkas cruising around and it will not last indefinitely against their 23mm autocannons.

Conclusion:  The Predator has gained a reputation as a fearsome weapon in Afghanistan, but that is a rural battlefield where the enemy is exposed to view from above and has no air defenses.  It will not meet with similar success in urban combat against a mechanized army that has vehicles hugging the vertical walls of buildings.  The Nona, though a bit outdated, accomplishes the same thing as the Predator at a fraction of the cost.  The U.S. Army would be better served by a modern self-propelled mortar such as the AMOS than by the Predator.  The 60mm is inaccurate because the base plate bounces off the asphalt and the 120mm digs itself into asphalt allowing the mortar crew to get outflanked, so the solution must be a self-propelled mortar.  Some people would point to the M125, but this is an antique that can be destroyed by every Russian vehicle in the field, even the BTR-80 with its new 30mm cannon, and cutting the roof off exposes the mortar crew to sniper fire from above; in a word, it is worthless. 

Imagine that perennial enemies Japan and China go at it. The Chinese put thousands of Nonas and Shilkas in the streets of Tokyo and the Japanese attempt to destroy them with U.S. supplied Warthogs overhead and Dragon missiles fired from the windows. Who would win?

Note that this question refers only to the weapon systems described, not to larger political/strategic questions or to the possibility of retaliatory strikes inside China.