I think of Soulknives less like Fighters and more like Monks, so I've never boosted their BAB- hit & run skirmishers, not toe-to-toe warriors.
However, I don't think it would unbalance anything appreciably if you did that (for either of those classes).
The one HR I have done consistently for Soulknives is I don't make them take the full round action to reshape their mindblade every time they manifest it- in effect, the blade "remembers" the last shape it took. Combined with the Soulknife Feats in Dragon #341, it adds a nice little boost without "stepping on anyone's toes."