As you mentioned, it probably does need to be a bit higher. The torcs, after all, make the Droods pretty much invincible. That is to say, the only thing that I can recall ever damaging an armored Drood was another armored Drood or, I think, the Deathstalker. Though I may be misremembering there.
Strange matter weapons can do it, like the elf arrow in the first book. Torc Cutter (from the first book) can kill an armored Drood, but it's a REALLY epically powerful magic item -- it's in the same 'forbidden weapons' collection as things like Sunwrack ('for putting out the stars one at a time') and Winter's Sorrow (releases Fimbulwinter - eternal worldwide ice age). In the second book (Daemons are Forever) the Loathly Ones can do it, too, with some of their top level weapons.
The veiling doesn't work for normal sight, IIRC, just magical detections. People do notice when they're armored-up in public.
No healing, yeah.
Supernatural Str/Toughness seem kind of low. An armored Drood can successfully wrestle a huge, age-old dragon and walk through ancient sturdy stone walls as if they were nothing; but Supernatural Strength might be OK, though at the high end of it. And Eddie Drood soaks up a (small, admittedly) atomic blast in the first book. Mythic Toughness at minimum.
It's not really an Item of Power, as the Torc can't be removed in any normal way without death
though the end of the first book does remove the original torcs via the death of the entity sponsoring it.
I agree that Sponsored mechanics are perhaps more appropriate, but they're really only designed for spellcasting.
I'd give the basic armor/torc:
The Sight [-1]
Human Form [+1] affecting:
Environmental Immunity [-??] Completely unaffected by any kind of environmental hazard (cold, heat, airless environments etc)
Mythic Toughness [-6]
The Catch [+0] Strange Matter and the like
Supernatural Strength [-4]
Inhuman Speed [-2]
