Everybody wins if ambiant magic goes down in Bretonnia. And considering how much that nation values honor, I wouldn't worry too much.
Also, almost everyone else has had to be "bribed" in some way in order to be brought into the project. Doing odd jobs for the colleges, clearing an important threat to Kislev, doing SOOO much for the Karaz Ankor, allowing Laurelorn to host the project, etc. I don't think it's a bad deal to gift tributarie in exchange for goodwill, it's not like we lose anything by acting for the common good.