What are the effects of meteor showers?

Very little, apart from giving a few people some good reason to go searching in unpopulated areas.

They have also added to our knowledge of the early solar system and also the composition of Mars in the early stages of formation.

I suppose in a *very* small way they have added to the mass of the Earth - possibly a couple of tons per year, but we have "ejected" far more than that back into space.