Successive ionization energies (work functions?) for metals
In an infinite metal solid, there are an infinite number of electrons, so each one removed will be at the exactly identical work function with no change in energy.

Intuitively, this may seem a bit strange because .. well, it should be harder to remove an electron once positive charges start to accumulate.

If I have even a micron-sized piece of metal, that's ~$10^{13}$ atoms. So you really have to do a lot of ionization before you're even going to get 0.1% of the metal ions.