Well... Main idea behind driving shield is to have low impedance shield arround sensitive high impedance wire with same potential as that wire. Having low voltage means that leakage current I=U/R will be low as well, even if insulation beween two isn't perfect. If you are measuring 1nA with 1% accuracy it would mean that if everything else is ideal, you have 10pA of leakage to play with. If all sources of leakage combined exceed this you have to guard against that leakage.
So if you are confident that common mode voltage beween your input and earth divided by insulation resistance between them would not exceed your current leakage budget, you don't have to drive it. Otherwise, idea is something like this:
This could be acomplished in various ways, so this might or might not be perfect for you.
Same idea goes for twisted pair: if your differential voltage divided by .... blah blah.. you know the rest.
You are right that twisted pair would be more resistant to radiated noise, as surrounding objects could not disturb balance between wires so much as with straight ones. So if you have differential voltage in mV range, I would say go for it. If differential voltage is high and you could exceed your leakage budget then go for separate driven coaxes as it's drawn on your or my schematic.
Two 2G resistors are more an option in my application, but they are there for case if very high impedance current source is used, like if you measure static electricity in air with pick up plate. Amp that I used has so high input resistance that potential could slowly rise as it charges input capacitances and would have nowhere to go, and it could easilly exceed voltage range of amp. Those two resistors provide a path for current to go through. 4G differential impedance is more than enough for my application
Don't forget to reduce bandwidth and input impedances to just what is needed, as thermal noise Vrms =√4kBTR
Hope this is helpfull, feel free to ask. That what's this board is about.