heedm,
You are correct that once stabilized in an appreciable vertical climb, the power is less than that you would need for the same climb done at Vy, but all climbs need more power than steady level flight. I have done some careful work to see what it takes to make a vertical take off as compared to a steady HOGE, and I have never successfully risen above about 2 rotor diameters without using 1.5% more power than the power needed to HOGE. Even with that 1.5% more, the climb rate was a paltry 50 feet per minute.
PPRUNERS, Give it a try. Take a very still day, and just HOGE at 1.5 times the rotor diameter (65 feet for an S-76, for example) and carefully note the power. Try to have no climb or descent, it might take a little averaging of the torque swings. A good way to do it is to release the collective, and just see if you average a nice HOGE, rather than get involved in a nice pilot-in-the-loop oscillation. Radar altitude really helps here. Set back down to a low hover and then pull exactly that power. In my attempts, I could only climb slowly to a few feet above the 1.5 diameter, then watch as the aircraft bobs up and down in neat altitude oscillations around the hover height.
I could only avoid this oscillation by starting all over again and using about 1.5% more indicated torque (actually 2% of the power I was pulling, ie 2% of 75% total torque). If I pulled the extra power, I slowly and steadily climbed right up to several hundred feet.