We tint finished all the time for people that want the bass to look as close as possible to it's aged condition. The rubout looks very good, I don't see many others get that detail as good as we do.
It's actually not about the product still functioning as intended. It's because about 30% of the older models have the pickups matched well enough to have tolerable levels of noise. We traditionally didn't do any matching, because the pickups all had the same number of turns on the coils. However, because the amount of copper varies in the wire draw (the same length of wire will have a different number of copper atoms in it), that level of matching isn't always good enough in the much noisier environment of today. The upgrade goes way beyond the noise level floors and makes instruments quieter today thatn they were decades ago in the quieter environment decades ago.
Even if an instrument is quiet, I would not rely on a non-upgraded Series I or II as my sole instrument on a gig. I would take a backup in case conditions change because even the same location will change over time so a previously quiet place may require you to face a certain direction to be quiet.
