Hi Loris,
I had the same experiences with the gold chloride addition to Ziatype (that is the reason I had some left in my drawer). In general I find a development process to give me a better tonal scale and abandoned any Pt/Pd print out process. For these tests I was using ammonium citrate as a developer.
I made more tests on some paper samples +/- the addition of HAuCl4 to the sensitizer(NH4Pd). There was only minor effects on Awagami Masa except slight reduction of printing speed and with Cot-320 a slight reduction of contrast. On Zerkall book and especially with Kozo I got much smoother mids and highlights. Herschel is already quite good without it but also got even smoother. The color change towards cooler and more neutral is at the concentration I was using it similar with all papers (most pronounced with Cot-320).