The weapon special ability ghost touch doesn't allow the wielder to make incorporeal touch attacks
That last sentence isn't the extent of the description. In its entirety, the weapon special ability ghost touch says
A ghost touch weapon deals damage normally against incorporeal creatures, regardless of its bonus. (An incorporeal creature’s 50% chance to avoid damage does not apply to attacks 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 either corporeal or incorporeal at any given time, whichever is more beneficial to the wielder. (DMG 224-5)
When the text says, "Essentially, a ghost touch weapon counts as either corporeal or incorporeal at any given time, whichever is more beneficial to the wielder," the text is clarifying, providing the reader with a summary of the weapon's fundamental functions that have already been described. It means the weapon strikes foes despite their corporeal states and the wielder can continue to use the weapon despite the wielder's corporeal state. Nothing more.
As you've noted, taking that last sentence out of context makes the weapon special ability ghost touch way more powerful than it should be for its +1 bonus.
The weapon by that sentence isn't given additional properties beyond what's already been described.
The MM and DMG agree that an incorporeal creature's physical attacks (whether with a ghost touch weapon or not) ignore non-ghost touch or non-force material armor
In addition to the Monster Manual's description of the subtype incorporeal (310-1), the Dungeon Master's Guide on Incorporeality says that
The physical attacks of incorporeal creatures ignore material armor, even magic armor, unless it is made of force (such as mage armor or bracers of armor) or has the ghost touch ability. (DMG 295)
So, while it's a little weird that a ghost (or an unbodied) can pick up from the floor a +1 ghost touch longsword and, bypassing the dude's full plate, stab the dude to death with that sword, that appears to be how it works. But were that sword not to have the weapon special ability ghost touch, the ghost would just look at the sword on the floor with despair. Okay, even more despair ('cause it's a ghost).
Best Answer
A magic weapon that possesses both the brilliant energy and ghost touch magic weapon special abilities ignores nonliving matter yet affects incorporeal creatures normally. Further, according to this Paizo blog post, a weapon that possesses the quality trip—like a halberd or whip—can also be used to perform the combat maneuver drag.
In combination, a creature using, for example, a +1 brilliant energy ghost touch whip can take a standard action to make a combat maneuver check that provokes attacks of opportunity against the square that the creature thinks her foe occupies. She makes a normal combat maneuver check against the foe's combat maneuver defense to drag her foe except that, because of the foe's total concealment, the drag maneuver has a 50% miss chance. If she's successful, she'll pull that incorporeal creature out of its space within the object to the adjacent space where the incorporeal creature can be dealt with normally.
Note, however, that a +1 brilliant energy ghost touch whip—despite costing 72,301 gp—is useless against incorporeal constructs and undead. You'll need a different tactic for ghostbusting or Vision-wrangling.
Of course—because Pathfinder—, casters can do this better: a similar weapon can be conjured with the 2nd-level spell ghost whip.
Note: I look forward to other answers. This is an already complicated problem made worse by the incorporeal creature having total concealment provided by the object! Also, thank you, ShadowKras, for suggesting the ghost whip spell.