Would resizing the sky sphere " Making it Smaller " affect the Performance " for the better" or it makes no difference?
I would be surprised if it mattered, as long as the size is reasonable. The resolution of the texture will affect performance.
scaling a mesh within normal operating sizes wont effect performance at all, its all vector data, points in space that cost the same to render at any size, however if you start scaling to small, you will get to a point where vertices of the mesh occupy the same screen space, which i believe will degrade performance.