All of the suggestion seems pretty OP. Better scaling and affected by Dex' Crit chance should be good enough imo. Maybe EMP knife to deal with robots (since there's EMP bolts, anyway), serrated throwing knife is also cool
Throwing gloves would be cool idea, which acts like Psi-band, improving throwing knife damage as well as throwing skill / crit chance / crit damage mod (for lore / game logic, it's a replica of ancient artifact known as P1P-BOY, an AI used to help aiming)
Feat-wise, I think throwing feat is good enough, the problem comes from low damage, which in turn makes fighting heavy armored guy a chore, since it can't even penetrate DT to makes use of poison proc (although ignoring mechanical DT/DR is absolutely OP)
Also, versatility affecting throwing skill would be OP, since it'll saves loads of throwing points, which essentially makes the skill redundant and makes any non-full-psi build has essentially super accurate throw.