I have to disagree, JiB. You're seeing this book in the light, I think, of the later books. But at this early stage of the Watch Books, I don't think Terry is writing about Power. And I'm not at all convinced by your attempt to see this as a struggle for political power.
Rather, I think that in this book Terry is exploring the possibilities of continuing to develop the Watch series as a vehicle for more serious exploration. After all, it's six years since he wrote G!G! and he's gotten his feet wet with more serious satire through
Small Gods, Reaper Man and
Lords & Ladies. But in this book, he is exploring what is possible with the characters--what works and what doesn't. That's probably part of the reason that none of the characters behave in any other book quite like they do here.
At the simplest level, Colon and Nobby are still funny, but not in the way they were in the previous book. And Nobby taking control and getting them into the armory is startling to the reader and to all the characters. Carrot, though he remains a flat and unrealistic character shows more depth in this book than he ever does again. Vimes goes through a crisis of change. He doesn't like the way he has lived, and he still thinks he's not worth much, but he does realize how much the Watch and being a Watchman means to him. Sybil notes the change just before Carrot turns up with the final resolution.
Sybil Vimes, nee Rankin looked at him with an expression of faint concern. For as long as she'd known him, Sam Vimes had been vibrating with the internal anger of a man who wants to arrest the gods for not doing it right, and the he'd handed in his bade and he was . . .well, not exactly Sam Vimes any more.
Vetinari learns that he is not as invincible and invulnerable as he thought. And he has a bag leg to remind him of it, and of the horrible mistake he made in dealing with Vimes and the Night Watch. He has learned that Vimes is no clockwork policeman, but a man who will take responsibility and act on it.
And The Gonne is the catalytic character that brings this all about. It is rather like the spirit of music in
Soul Music in that it bends the possessor to its will by any means it thinks will work. I suspect that it knows when it's beaten--because Carrot has just stabbed Cruces through the stone. But even he picks up the gonne by the barrel and immediately destroys it. Though it's not entirely clear, I suspect that the "evidence" and the "gonne" have been laid to rest with Cuddy.