Why don't we try something like this? I didn't see evidence that they stop being fully ethereal when fully manifested, either, so I changed that for simplicity.
Creepy (Su): A spectral wizard, even when fully manifested and corporeal, never makes noise without choosing and may move silently at will.
Manifestation (Su): A spectral wizard normally dwells on the Ethereal Plane where, as an ethereal creature, it cannot affect or be affected by anything in the material world. However, a spectral wizard can partially or fully manifest on the Material Plane. It takes 1 move action for a spectral wizard to partially manifest and 1 full-round action to fully manifest. It takes the spectral twice as long to manifest in areas of bright light, such as daylight or a continual flame spell. A spectral wizard may un-manifest as a move action.
A spectral wizard has two home planes, the Material Plane and the Ethereal Plane. It is not considered extraplanar when on either of these planes. Manifested spectral wizards can be attacked by foes from either the Material or Ethereal Planes, but are somewhat protected by incorporeality unless fully manifested.
When a spellcasting ghost is not manifested and is on the Ethereal Plane, its spells cannot affect targets on the Material Plane, but they work normally against ethereal targets.
A partially manifested spectral wizard becomes visible but incorporeal on the Material Plane. It can pass through solid objects at will, and has an incorporeal touch attack. Its incorporeality protects it from foes on the Material Plane, but not from foes on the Ethereal Plane. Its spells continue to affect ethereal targets and can affect targets on the Material Plane normally unless the spells rely on touch. A partially manifested spectral wizard's touch spells don't work on nonethereal targets.
A fully manifested spectral wizard has assumed physical substance on the Material Plane and loses the incorporeal subtype. Fully manifest spectral wizards have no incorporeal touch attack, but can manipulate material objects, wield weapons (using Str to modify melee attack rolls), grapple creatures, and cast spells, since they are corporeal. Fully manifested spectral wizards are also affected normally by non-magic weapons and mundane fire, cold and acid, but they retain their deflection bonus to AC and remain weightless. Despite being corporeal, spectral wizards are still etheral and interact normally with foes on the Ethereal Plane. Its spells affect targets both on the Material Plane and Ethereal Plane normally.