IMHO: a lot depends on how long the project goes for. As you know, clients prefer to pay for what you already know, rather than pay for you to learn on the job. So this could be a golden opp to get some PM experience on your CV to act as a stepping stone towards a client-facing project management role. Unfortunately, in some offices, an internal project can also be the equivalent of being posted to Siberia. The longer the project goes for, the more possibility of being sidelined and forgotten. On the other hand, it can also increase your visibility to Partners that you don't normally get to work with. I can't comment on the politics at your office, but maybe you can find a trusted mentor in the office where you work.
