The magic of the setting in The Dresden Files is highly tuned to the individual practitioner, as Harry states several times in the books. As such, the magic system in the RPG is tailored to this.
I recently had a Spirit Evoker, and that was a problem we had, especially as a person new to roleplaying. What we had to do was to talk about the character and what he was trying to do that would give him the idea that Spirit was the way to go for this particular wizard.
In his case, he wanted to play someone that had been tempted by necromancy, and still had the miasma of that experience clinging to his magic, and permeating his aura. The other thing he wanted to bring forth at times was that it was an encounter with the spirit of his lost love that had brought him back from the edge.
That shaped his rotes and the spells that he used, from a Kinetic Shield rote to the Miasma of repelling that he used for his veil, to the Soul shard that he used for his major offensive spell. In the end, he used specializations in Spirit, his Conviction, and his Discipline to fling spells, just as a Fire Evoker would do. The rules support the magic- they don't define it.
A little later, when the Warden was killed, he used some things he had gathered to call up the Warden's shade in order to question the Spirit. His background in Spirit magic was more of a permission for this knowledge, rather than a rule that surrounded the use of it. In the end, it was a standard thaumaturgic ritual. Again, the rules support the magic- they don't define it.
Concentrate more on the narrative, and the idea that the magic of Spirit is that of pure magical essence and the intangibles of that sort of power and you'll make not just a generic Spirit mage, and more of a Spirit aspected character that has a magic that reflects his background.
TL;DR - The major point is that the magic, just like everything else, should follow the narrative, rather than the other way around. Create a practitioner that has a story around his use of Spirit magic, and the actual spells used will flow from that source.