OK, the D70 dark image issue mentioned elsewhere is fixed; at some point I set the exposure compensation to -2.0 and never returned it to 0.0.

Apparently exposure compensation is a global setting, meaning when I used it in Program mode and switched over to Aperture Priority, for example, the EC setting was still -2.0 and didn’t reset itself like my Canon does. While annoying (all the photos I shot in Curacao suffered from this oversight) it’s another thing I’ve learned and won’t forget again.