Book 6. You basically get upgraded versions of all the abilities, plus one extra I think. (Nexus, which lets you resist the elements.)
You keep Mind Blast, but also get an active attack called Psi Surge, with gives you +4 CS at the cost of -2 EP every round of combat.
As you get additional Kai ranks in the Magnakai series, what each ability is capable of doing expands as well. (Also dependent on what Lore Circles you have completed.) Lore Circles are CS and EP bonuses you get for having certain combinations of disciplines. (Circle of Fire is Weaponskill, Huntsmastery and Pathmastery, iirc.)
Then in Book 13, you get another upgraded set of core abilities, plus Alchemy and Meta Magic. And abilities upgrade within the Grandmaster series as you gain more ranks too.
What's cool about the upgrades is that they all play into how Dever tells the story. Camouflage, instead of just being you being good at hiding in bushes and shadows, becomes full blown invisibility. And then it gets better by you being able to mask your body heat, scent, and eventually all sound. Huntsmastery eventually gives you telescopic vision, and other stuff I can't remember. Curing not only heals you, but you can start healing other people's diseases, purge your body of poisons, ect...
Like I said, by Book 20, you are literally a god.
While it's not hardcore RPG stuff, it still gives you the sense you're becoming better, and allows you to trivialize a lot of threats that a younger Lone Wolf would have had to confront. It also makes for more diverse stuff that Dever throws at you.
So you start seeing stuff like:
A Zornath, a vicious night hunter with preternatural senses, guards the only exit from the dungeon.
If you have the Magnakai Discipline of Invisibility, AND you've reached the rank of Guardian AND you've completed the Lore Circle of Spirit, turn to page 55.
If you don't not possess this discipline, the Lore Circle or the correct rank, turn to page 132 to battle the fearsome Zornath.