I know this will probably come as a surprise, but I'm actually leaning toward straight-ahead monster with PLAs as well!
OK, stats somewhere between a Wraith and a Dread Wraith?
The Psionic Spirit's AC 0 equals AC 20 in 3E, halfway between the AC15 Wraith and AC25 Dread Wraith's 16HD, and its HD is inbetween as well (9HD vs 5HD & 16 HD).
Averaging the two Wraiths:
Wraith: Str —, Dex 16, Con —, Int 14, Wis 14, Cha 15
Dread Wraith: Str —, Dex 28, Con —, Int 17, Wis 18, Cha 24
Psionic Spirit: Str —, Dex 22, Con —, Int 15, Wis 16, Cha 19
That looks fine to me.
The original could only attack with its psionic powers, do we want to keep that or give it an incorporeal touch of some kind?