Your arguments for and against don't exclude each other, I feel they are complementary.
Wizards stick to their own world as much as possible, and mostly wear their own clothes. When/if they have to go about in the muggle world they sometimes "disguise" themselves as muggles, but this doesn't happen very often. You mention the railway station, but there are other means of transport as well, that don't require putting on muggle clothes. The man at the Quidditch world cup probably avoids the muggle world as much as possible.
Also when a witch or wizard has to do something on his or her own in the muggle world, they can just keep on their robes and raise an eyebrow or two on their way, but much more won't come of it.
For larger events as the Quidditch world cup, where whole crowds of wizarding people have to gather, it might be customary or even required to put on muggle clothing to not draw attention to the high concentrations of wizards in one place.
The link to the SciFi-SE that @Scorch91 commented (Do students wear muggle clothing while not in classes at Hogwarts) also has some interesting and related views and information.
If you think about it, it is not just the clothes. The wizarding world in general is hesitant to adapt things from muggles. When Arthur Weasley created the flying car, it was considered abuse of magic and was frowned upon.
They do, however, use a the Hogwarts Express, which is a train, created by muggles.
They also adapted to use cameras for taking pictures, also a muggle invention. The cameras used were magically enhanced and then they stopped following the new muggle improvements (at least in the movies, who knows what kind of camera J.K. Rowling had in mind).
In my eyes, the wizarding world finds it difficult to admit that muggles have a good idea every once in a while.
The flying car was a hit and miss, but if Arthur Weasley fiddles around with some more muggle appliances, who knows, he might find the next proverbial camera.