hmmm, I ride in snow about 2-3 times a week, never seemed to have a problem with getting snow into the fork, maybe I am too old and slow or just don't ride in deep enough snow
The performance of the fork definitely slows with colder weather, but not too bad, guess it depends on just how cold it gets.
Riding in wet snow is almost like riding in mud, the snow can collect in the drivetrain and cause issues.
Clean the bike reqularly and lube very ofte.
As for lizard skins, just be aware that any water that gets behind the skins will be kept there and could cause the very problem that you are trying to prevent with the cover.