PBW should be completely safe and effective, at recommended concentrations, for cleaning those. I think the reason you're seeing fading of the gold is that the contact time is too long. Next time a 5 or 10 minute soak, followed by some light scrubbing if necessary, should work just fine.
With basically all chemical cleaners the important factors that increase cleaning power are time, temperature, pH/concentration and mechanical action. Increase any of these and you'll increase the effectiveness of your cleaner. These will also increase the susceptibility of metals to chemical attack.
PBW does say that it's "safe on skin as well as soft metals such as
stainless steel, aluminum, and on plastics" but in my experience, stainless steel is the only material that's truly impervious to basically anything you can throw at it (with some exceptions, such as chlorinated cleaners and highly concentrated acids). Also I'm not sure I believe when they say that stainless steel is a 'soft' metal...
I guess it all depends on what the 'gold-tone' coating on these is. Perlick uses PVD (physical vapor deposition) on their gold-tone taps and as far as I could find, the most likely material for PVD coating in gold-tone is titanium nitride, though this seems like a pretty tough material. It could also be real gold, which is also highly resistant to corrosion, though this seems less likely than the other option.
Anyway, the real point is that you now know whatever makes these gold doesn't stand up to extended stays in PBW. Again I think cutting the contact time way down should keep the gold coating intact and still provide you with effective cleaning power. The real good thing is that, if it is in fact stainless steel underneath, that's not going anywhere for anything.
EDIT - I came across something interesting reading the patent for PBW. If you go nearly to the bottom, in example 4, you'll find data saying that PBW caused corrosion in brass at a rate of 11 PPM (at regular concentrations, over 20 minutes). Earlier in the patent it mentions that it "does not corrode or scar metals such as aluminum, stainless steel, and brass". So I think it's important to realize that, when they say it's 'safe' to use, it doesn't mean there will be no corrosion, but rather only very little corrosion. This corrosion is inconsequential with a solid piece of metal, but when you're talking about a 0.25 micron-thick decorative coating it suddenly becomes much more important.
Now your faucets may not be coated in brass, so this might not apply directly, per se. But it's definitely true that, with non-stainless-steel metals, the safe use/compatibility with a cleaning product may (and in this case clearly does) involve a certain, albeit very small, amount of corrosion to that metal.
So, taking everything together (a very thin layer of not-fully-corrosion-resistant coating being left to soak for a long time in a very-slightly-corrosive solution), you can probably begin to see an explanation as to why the gold-coating on these taps did not last.