Boosts can be quantified using damage from offensive discs. Healers get a 6 skill boost at skills 24, 25, 26, and 27, and a 4 skill boost at skill 28. Skill 29 and 30 are normal skill levels. So if you take a disc that does a specific amount of damage per skill level like assault, you get damage numbers that look like this:

skill level 21 - 252 .............................effective skill level: 21
skill level 22 - 264 (+1 skill) .................effective skill level: 22
skill level 23 - 276 (+1 skill) .................effective skill level: 23
skill level 24 - 360 (+1 skill) (+6 boost) ..effective skill level: 30
skill level 25 - 444 (+1 skill) (+6 boost) ..effective skill level: 37
skill level 26 - 528 (+1 skill) (+6 boost) ..effective skill level: 44
skill level 27 - 612 (+1 skill) (+6 boost) ..effective skill level: 51
skill level 28 - 672 (+1 skill) (+4 boost) ..effective skill level: 56
skill level 29 - 684 (+1 skill) .................effective skill level: 57
skill level 30 - 696 (+1 skill) .................effective skill level: 58


These boosts affect all damage discs, area and direct. They also appear to affect more abstract discs such as stun and charm. It could therefore be assumed the boosts would also affect aid.