Powergaming Pixie, ...just some thoughts. Options

[Machiavelli]

Imagine the following situation and tell me what you would think of it:

Pixie with magician or mystical adept quality. Owns a level 3 sustaining focus and depends on a possession tradition. Now it casts a shapechange spell (human) which should cause in physical attributes of average 3 and +1 for every hit he casts . Spell is put on the sustaining focus and tadaaa....you have a very skilled magician in human form with innate concealment power and none of the disadvatages of the pixie (size and fragility) any more.

Is that too much?^^