There's good patina and bad patina when it comes to vintage watches. Condition is everything. The Watchfinder photos don't really tell us enough about the watch - you'd really need to properly check it out, inside and out, before deciding it's worth. If Watchfinder have had it, they may have refinished the case in which case that takes a lot off the price. Burlington Arcade is also quite renowned for asking over the top prices, isn't it?
I'm confused, I thought these were way more than this? No?
Incorrect hands and the aforementioned dial discoloration will affect value. These days the market is way down from the highs, so while a perfect Monaco might still be up there anything that isn't a top specimen is nowhere near where they were