^ Whilst I agree slightly, I think a well themed one would improve the park.
In my opinion, it would draw crowds, but only if the theming is impressive (like Talocan). Plus if you have that dramatic theming, you then have your "killer image", as Varney would say. A ride that flips upside-down, has fire + water effects, and amazing theming would be easy to advertise. And more guests means more money for Thorpe Park, meaning they would benefit more than by adding nothing, unlike what you suggested And you said Rameses Revenge has short queues, well that's probably because the main audience of Chessington will rarely be interested in an intense ride like Rameses!
That's just my view though.