As a person who doesnt make mods, im not sure how difficult this would be. Maybe instead of changing the way the spectres gain influence, you could add a new adversary just for them. I have a few ideas.

Saren (or other major bad guy) - just a suped up version of the turian soldier with a lot of useful abilities.

Cerberus/Collectors/Geth soldier squads - instead of just one chosen, you could have a chance to spawn a special strong squad of units.

Again, just an idea. ultimately the mod maker gets to choose what to do.