Kind of hard to say without seeing the dagger.
To remove a little dirt or grime, a VERY light and well done removal would seem ok.
To remove that green verdegris is also a good thing. it eats everything.
To remove any tarnish, you will always have the "CLEANED" look that you do not want.
Just gives me the creeps when I see a dagger, or a fighting knife that has been all cleaned up.
Ed