I am an unsophisticaled DIY'er, but I would guess that the cooling SEER of a air heat pump could be improved by adding water misters to the outside coils.  If the water is 50 degrees F, evaporative cooling should make the heat transfer much more efficient.  Has anyone tried this and how well would it work?

Scroll to the bottom of this page or here.  There are also commercial versions available.  Performance will vary with outdoor relative humidity & temp, but the principle is sound. (Don't bet on 30% though, marketing claims notwithstanding.)