I've noticed this too since loading Seasons. The first thing I did is create a Sim and put him on a lot on the island in Windenberg. The island has been my absolute favorite place to play since getting GT, exactly for the reasons mentioned above. Up until now, it's always been so peaceful and deserted, no walkbys at all. The only sim I'd ever see was the mail person.
Now, I get constant walkbys such as Mila Munch, Hugo Villareal n his Scout uniform, Marcus Flex jogging, vampires and wannabes at night, etc. They'll even sometimes stop and make Snow Pals. My Sim's lot is starting to be surrounded by an army of them.
It's rather annoying, but not so much I don't want to continue using the island. I love that island more than any other area/neighborhood in the game. Except perhaps Sylvan Glade. So far that area seems to be relatively untouched by the weather except in Winter no fish are jumping in the water. You can still fish there and catch them, but you can't see them.
Plus, certain plants are just mounds of dirt because they're 'dormant.' That was disappointing. I went there specifically to collect Lilies for my gardener Sim. I guess he'll just have to wait until they're in season. I thought Gurus said that the hidden areas wouldn't be affected by seasons? Maybe I misheard and they said/meant the weather. I guess that makes sense. Perhaps it's challenging/not possible to exclude the affect on plants just in certain areas. Bummer... Oh well.
Happy Simming anyway! <3