Is there another instance of a king being called Gracious? It’s a little odd. Your Grace, okay. I get that. But gracious? I guess it falls in the same category as Majesty? Like it’s a hipper way to say, “Your Grace”?
I’m tempted to re-punctuate this bit. To have “gracious” be a compliment that Polonius gives his daughter, a reflection of how he perceives her walking there. And even “so please you” could be to Ophelia. It would soften the relationship between Polonius and his daughter a little bit, maybe give it a shade of affection, as if he were asking her permission to hide with the king or at least just letting her know where they’re hiding. That would give a fun bit of business for Hamlet and Ophelia later when he asks where her father is.
It could be. “Gracious! So please you, we will bestow ourselves.”