Unfortunately I can't really draw any conclusions. After I applied the aspirin solution, the weather improved and we had an extended period without rain. The fungus even on the untreated leaves died off in the drier conditions, so I can't say to what extent the aspirin worked or not.
But plenty of people on gardening forums swear that it works, and I will try it again if I have this problem next summer. Growing conditions were just poor in general this season. Way too wet. My pumpkins are quite a bit smaller this year, and I think it's because the plant was having to devote so much energy to growing replacement vegetation.
I don't even do anything edible with pumpkins. I grow them for the hell of it, and because they make nice targets at the shooting range.