The vault guardian is also extremely fast, and imposes a -3 penalty to all surprise rolls when defending its charges.
Perhaps a Dex boost as well?
The attacks of the guardian can reach into the Astral and Ethereal Planes and can injure those struck only by magical, silver, or iron weapons.
A vault guardian takes no damage from normal fire, magical fire, or cold-based attacks, and electrical attacks cause only one-quarter damage to the construct. Charm and sleep spells have no effect on the vault guardian, nor do other mind-affecting spells or any poisons.
Because of its construction, the vault guardian is vulnerable to earth magic. A rock to mud spell inflicts 2d10 points of damage on the creature and stops it from moving for one round, and earthquake or stone shape instantly kills the construct (no saving throw allowed).
Detect Intruders (Su): Vault guardians continuously use detect magic and true seeing as the spells (caster level xth).
Besides the ghost touch, should we also treat their attacks as magic, silver, and cold iron for purposes of overcoming DR?
Should we go with the nontraditional (for a golem) immunity to cold and fire, resistance to electricity, and vulnerability to earth magic, or pigeonhole it into the more traditional immunity to magic?
Shouldn't the NA be +8 to match the original AC? I'd go with DR 5, since the rest of the stats suggest a CR around 5 or 6.
I'd be OK with a NA of +12 to +16 to bring it more in line with the CR.
EDIT: We could also reduce the DR from 15/adamantine to 10/adamantine to go along with its lower HD and CR.