The Harpells were always a little quirky in their spellcasting, so yeah, the rules in Wild Spellcraft could definitely help. I'd encourage you to use the exotic and bizarre mishap rules (the tables that have the whacky results).
However, Wild Spellcraft also has a good deal of info on new spells that fiddle with chaos, randomness, and probability. Though the Harpells are not your standard wizards, they didn't precisely try to master wild magic. Thus, not all of the book would be appropriate for the Harpells, but I'm sure you'd be able to find uses for it.