Well I asked about this, and a 'direct' application of nanovolt measurements is sintering. Apparently you can measure the conductivity of materials as they are being sintered to get the proper 'bonding' or whatever you want to call it. Like powdered metal parts (titanium, stainless, so forth)
That sounds like something useful for DIY parts. That's what I was getting at, can this enable you to do anything NEW, not slightly better. The problem for me is that I have a DSA already (and you can get them cheap sometimes, like me), and yeah.. maybe it could lower the noise floor a little if you made it, but damn I just don't feel compelled. The whole making a seismograph/sensor is actually the hard part (its almost always precision expensive mechanical engineering that you need to benefit from these parts).
Experiments with strain sound possibly cheap (maybe just a heavy screw and a heater would be enough with a crude die. At least it does not feel like a mega project to think about compared to some other nanovolt things, since you are just essentially measuring a resistor directly.