I think the SLAs are mostly good enough for illusions, but I like what you have some more. Filling in the rest...
Spells: A ruler aboleth casts spells as a 20th-level sorcerer.
Sorcerer Spells Known (6/8/8/8/8/7/7/7/7/6, save DC 18 + spell level):
0—arcane mark, dancing lights, detect magic, ghost sound, mage hand, prestidigitation, read magic, resistance, touch of fatigue;
1st—chill touch, color spray, mage armor, true strike, ventriloquism;
2nd—blur, daze monster, mirror image, misdirection, touch of idiocy;
3rd—dispel magic, dispacement, haste, rage;
4th—black tentacles, confusion, crushing despair, enervation;
5th—cloudkill, feeblemind, mind fog, waves of fatigue;
6th—control water, greater dispel magic, true seeing;
7th—finger of death, greater teleport, insanity;
8th—demand, mind blank, moment of prescience;
9th—foresight, power word kill, time stop.