Too Few Characters?

My reading pace has slowed down from a sprint to a stroll lately, but Sourcery sags in the middle.

Things are happening, and events are being put into motion,  but it's all happening at what seems to be a snail's pace. The best reason that I can come up with for this is that Pratchett doesn't have enough perspective characters in the book to work with to advance things along varied strings. Or, at the very least, he doesn't mix up the order of perspective characters very well in this book.

Generally speaking, Sourcery flows something like this: Rincewind and Conina, the Wizards, the general populace, and repeat. Later Pratchett books are bristling with characters, each as sharp as the last, who all contribute their own bit to the overall plot. The sort of plodding onwards that Sourcery delivers, though, falls short of what I expect from Pratchett.

Still, the jokes and asides are entertaining and interesting, so I'm willing to press onwards. Even if Rincewind and Conina's plot is taking far too long to fully develop.