Yes they may be effected by choice of paper, but I suspect that this is because of the way platinum reacts to different papers rather than any impurities in the paper.

Platinum and palladium are similar but not the same. For example, gelatin binds to platinum and stops it producing an image, but it doesn't bind to palladium. So a platinum-friendly paper would naturally show more plague spots than a paper which is not (assuming there's platinum in their coating).

Platinum also tends to create a more gritty image than palladium (which normally has a smoother transition of tones). It's possible, although this is speculation, that platinum naturally produces more spots than palladium.

Because most people nowadays print with pure palladium or palladium-rich solutions, and because so few papers are platinum-friendly, I wouldn't be surprised if this is not much of a problem for many printers.

Additionally, when prints have a full range of tones, or lots of dark areas, then many of the spots wouldn't be visible unless you know what to look for.

I'm interested in what you say about pre-acidification. When I tried this the number of spots on my prints increased dramatically, so I stopped quite quickly. That increase would point to one of two things, either: (1) increasing the acidity of the paper increases the frequency of spots; or (2) I was somehow introducing pollutants during the pre-acidification, and these led to more spots. I don't know which of these is correct and have no evidence either way.