Amsoil, Redline, Sweet, Pentosin, RoyalPurple, JoeGibbs, Wynns, BG, Bardahl, Gunk, Synlube, Lubro-Moly.... all have synthetic power steering fluids.
If you use a quality name brand synthetic PSF, there is NO need for any additives.
Synthetic fluid works great in cold climates, like NY winters. PSF is also a rarely maintained and is usually an unfiltered fluid. A synthetic is an easy 1st upgrade. So, synth is not a waste.
If you use a generic PSF, like whatever is on the shelf at your local department or automotive parts store, then I'd recommend dosing it with Lubegard. I'd only recommend Lucas for warmer climates and for leaking pumps as it is very thick.