Caster level, sure, through the roof.
Spell level ... 20th level, or 2,000,000th level ... he's not gonna use Heighten to set the spell level above 9th. Heighten can't do that. Just like Maximise can't make you roll 20's for dispel checks, even if you prepare a "maximised greater dispel magic" or some such.
HE could set the level for almost EVERY spell he had prepared, that had a saving throw, to 8 or 9 ... fine; and that'd be pretty powerful in it's own right.
But a 20th level spell, through Heighten Spell?
Not.
Physically.
Possible.
Pre-ELH, there's no such thing as a 20th level spell. Post-ELH, you need Improved Heighten to set spells at levels exceeding 9.
Spell level ... 20th level, or 2,000,000th level ... he's not gonna use Heighten to set the spell level above 9th. Heighten can't do that. Just like Maximise can't make you roll 20's for dispel checks, even if you prepare a "maximised greater dispel magic" or some such.
HE could set the level for almost EVERY spell he had prepared, that had a saving throw, to 8 or 9 ... fine; and that'd be pretty powerful in it's own right.
But a 20th level spell, through Heighten Spell?
Not.
Physically.
Possible.
Pre-ELH, there's no such thing as a 20th level spell. Post-ELH, you need Improved Heighten to set spells at levels exceeding 9.