Nnnnno. I agree that the Spirit of a City is going to be utterly unsuited for most applications, but mainly in the 'using a Thor shot to kill a pesky mosquito' sense. The concept of the Spirit of a City being 'fragmented' and 'so other' ... well, while it's an interesting thought, and in your game that may work, but for how Shadowrun has been stated 'to work, it isn't really correct. The fact that this exact thing was not only successfully accomplished in the 21st century, but done so at the same exact instant is part of the official metaphysical explanation as to how and why Denver became a fractured city - a simultaneous summoning of the City's Spirit (Zebulon) sundered it into several fragments, which is what Ghostwalker was doing for those first months in Denver, 'spirit-hunting' to put that Spirit back together again.
Every city has a 'core self-image'. If you want some place to start, start with their best-known nickname. The Big Apple. The City of Brotherly Love. The Mile-High City. Windy City. The Emerald City. New York, Philadelphia, Chicago, Denver, Seattle. Evolve from there: Seattle, especially in SR, is an outpost of civilization in a 'low-tech' area, a city under siege, the only city on the West Coast that's still UCAS amidst elven and Native American nations. It's also almost the only city in North America that has such an intense megacorporate focus on it; EVERY Big 10 (and a lot of other AAs) have a major structure in the area; even S-K has focus in Seattle, though they don't admit to it per se. It's the high-tech wild west, cybernetic cowboys vs. shaman-mystic indians.
Despite its gaping wounds in Redmond and Puyallup, the Seattle Metroplex is an intensely vibrant city with virtually one thing on its mind: success. Despite its history and age, it is young, intense, growing, eager to seize new opportunities, develop new ideas, constantly striving to create and break out and be the single most important city in the world. It wants to be New Mecca.
As a consequence, it DOES have a cumulative sense of drive, destiny, desire, and - yes - concern about 'most of the rest of reality', specifically the city of which it is the Spirit. And yes, there are vastly easier paths to take. But if you're the GM, and you have a group of NPCs that are off their rocker ... can you think of a better way to poison the entire town's essence than to turn the Spirit of the City toxic?