When I read the Watch books, I always think of Angua as Anjuna - a beach in Goa, India. It seems to me to be a better name for her.
I also pronounce Lancre as "Lankrur".
And Ford Prefect as Ford Perfect in Hitchhiker's Guide.
I don't think it matters how you pronounce characters' names, it's subjective.
And anyway, Americans are always pronouncing things differently to Brits eg; bouy, Derby, Arkansas, tomato, Iraq and Iran, zebra etc.