There are veneers, and then there are "veneers". True veneers are paper thin as you mentioned, and don't affect performance. Well, the additional glue required might stiffen the limb, but the additional weight of the glue might also detract from performance. However, some folks call the first lamination under the glass on either side of the limb veneers, regardless of their thickness. So, if the"veneers" are really just two more laminations, then yes, they will affect the bow's performance, etc.