I'm not even sure which side I would come down on if I had to make a GM call. The main fairness/unfairness consideration in my mind is that a starting, 6 magic, character can conceivably raise an attribute from 6 to 12, provided the target's augmented max is that high (and he could get the hits), but not raise a 7 to an 8. Especially in this example, where an Adept could theoretically sustain it himself with Living Focus. Living Focus can only Sustain a spell of force<=Adept's Magic. So if you have an extremely high augmented max, it winds up being beneficial to keep it lower so your Mage can boost it and so the Adept can sustain it. Of course if you can get your Mage to blow Karma on a Sustaining Focus, that's his problem. I'd love it if an Adept with Living Focus could pass the spell off to a Sustaining Focus but that seems like stretching the rules until they snap.
Edit: Elves are a perfect example. Keep CHA at 6 and it can be boosted to 12 by a starting Mage. Buy it to 7 or 8 and it can't.