The integral of - e.dl is the potential or ie. -* the amount of work done by a charge in moving through a distance of infinity to a point r,where dl is the path element corresponding to the line connecting infinity to your point r . if i were to calculate the potential at a point r+1 this would be lower than at point r as it moves through a shorter distance from infinity so i change my relative end position the charged reaches relative to a charge q. this is different then extending the wire. as by entending the wire you do not change the final starting point of a charge and end point. We know that the line integral from the positive terminal to the negative terminal (pd across the circuit) is PATH INDEPENDANT therefore increasing wire length does NOT decrease potential as the relative start position and end position for a charge moving through the wire is invariant
edit: ofcourse as commenter above stated... if the material has a polarisation to it as in a capacitor, then the resulting E field will decrease causing a lower potential difference, for a different reason to your first point stated
edit 2: commenter above is actually talking about losses in a wire due to heat. this is a pd difference across the wires. if your talking about the circuit then the pd across the Battery TERMINALS is invariant to wire length (ignoring polarisation