I must be missing something regarding the feat or the amulet w/ ghost touch.
A ghost touch weapon deals damage normally against incorporeal creatures, regardless of its bonus. An incorporeal creature's 50% reduction in damage from corporeal sources does not apply to attacks made against it with ghost touch weapons. The weapon can be picked up and moved by an incorporeal creature at any time. A manifesting ghost can wield the weapon against corporeal foes. Essentially, a ghost touch weapon counts as both corporeal or incorporeal.
To me the last line says it counts as both.