Ok after reading 6 pages of this thread I may be a bit lost, but couldnt Black Knights argument simply come down to this:
A cleric of 7th level can only cast 4th level spells. A persistent maximized empowered quickened 4th level spell of awesomeness is still just a 4th level spell.
That same cleric using DMM to heighten just by 1 is still casting a 5th level spell which his table strictly says he cant.
I mean technically, a first level cleric with DMM:Heighten can enter prestige classes that require you to be able to cast 9th level spells if the 2nd ruling is actually legal.
Not really siding with either side, just trying to simplify things a bit