I mainly fly out of a grass field that sometimes can be muddy even if the surface seem hard and aircraft doesn't sink in. From time to time (rarely but does happen) I would arrive back to field only to find my leading edges of wings and controls covered in chunks of already dried up dirt (indicating that dirt got on the wings during take off).
Technically the correct answer is yes - it will have an effect. In reality, as you already noted - you will not feel it.. As long as you don't fly close to stall speeds it should be fine. The thing about GA spam cans is none of their wings are really factory spec - all of them have some sort of bends, rivets etc that make them already imperfect, I think it's very unlikely for a thin layer of ice make things any more difficult to you. I have yet to find two C150's that stall the same way or at the same speed
but the emphasis here is, as already mentioned - when does it become too much? Although thin layer it self will not cause problems, that thin layer may have a tendency to start growing rapidly if the humidity is there to support it