do i under estimate Minor Globe?
if you can cast 9th level spells, is MGI a real concern?
If you're a "mailman" type, where your primary offense is a low-level spell with significant metamagic applied to it.
Even aside from that, if the Heighten is free then it saves you resources - often a lower-level spell would be sufficient if not for the globe.
Not sure I understand the OP completely - can you heighten any of your spells for free, or does this only apply to a single spell, like an Arcane Thesis type of deal?