Keep or sell - NX100
The main problem that the NX100 has is that it isn't much smaller than the NX11/20. That was always it's problem, it just wasn't that small.
I don't think you'd get much for it tbh, so it might be worth keeping because it has a different type of output to the NX20 and 1000. Also, as it uses the same batteries and charger as the NX20 it might be a viable back up camera to that.
I would keep it.
A little green rosetta......a tiny green rosetta........