Opinions of NX100

The nx100 is a great camera and the 20-50mm a very nice kit zoom. Looking at your gallery I notice that you have a canon 500d; I would expect the iso performance to be similar. If you're using the kit lens with the 500d then you'd find the Samsung 20-50mm to be superior.

Regarding whether to trade it for the sx50, well as I understand it the canon is relatively new and its second hand value is currently much higher than the Samsung (I paid £140 for my nx100 with 20-30mm second hand here in the UK), so although the Samsung is the better camera it's not a good deal. The nx200 is closer in resale value. Maybe sell the canon and buy the nx200 second hand.

All the shots on my gallery here on dpreview are with the nx100 with 20-30mm if you wanted to check out pretty much out of camera jpeg quality.