water doesn't get gloopy! Lol
Others have found that you can use less water in winter simply because it isn't drying out as fast, ergo the gravity draws more of the water down the glass and thereby taking microscopic particles with it, as against evaparating quickly and leaving them behind.
Winter weather IS dirtier though, more wind + more rain + falling leaves + road salt and so on and so on.
So what with spray from traffic getting pushed into the air from vehicles, all this muck gets into the atmosphere, blown around by the wind and settles on the glass
In summer weather it is dust that settles on the glass and frames, but winter much is going to be damp or wet, so it is going to 'set' onto the glass and be harder to get off than dust.
Make sure you rinse your frames thoroughly, particularly the top edges.
Most spotting occurs near the top of the glass, so this should really give you a clue as to where the small amounts of soiling are causing the spotting...usually from the top of the frames.
Ian