And totally new conversation portions for the entire game for him, and he's an active party member in the banter, and changes several portions if you have him with you, etc. I did my first playthrough without him, and it was ~very~ different with him in the party on the second trip.
WK was fun just for the boss fight, but I wouldn't have paid for it, but stone prisoner? Absolutely worth it.
To each their own, but for me I want extra playtime - I'm glad that party banter has made a return, but I don't want to pay for more of it. As for changing portions of the game - it's fine if you have Shale in the party, otherwise you miss out. The whole game can and does work this way, but with Stone Prisoner there isn't enough base content imo. I followed her dialogue and took her into <x>, but I found her lack of stamina problematic (didn't have the stamina pots mod at the time). Her footsteps annoy me anyway, so once that part was done she was out. I wish I could buy some pigeons to leave at camp