can Greater spell focus Illusion and arcane defense illusion give you an ability similar to a paladin's except that it can be used to detect invisiblity?...Or similar Illusion based spells?

Spell focus / defense: illusion needs not to be increased in power. They already raise the DC / protect against powerful spells. The reason some of the similar feats were bettered was that they barely had any spells affected by such.

For example Divination only granted a boost to feeblemind -a high level spell.

Abjuration has no or very little spells affected

Etc.

No.