The GTX 960 4GB is a little slower than a GTX 1050 Ti 4GB. While a mild upgrade over a GTX 1050 2GB. I could not see it being worth the cost.
The real advantage is the extra VRAM allowing for higher settings.
I suppose if you want to go through the risk and hassle of buying a used one off eBay. Then selling the GTX 1050. You'd be looking at a near even swap. Minus selling fees. I just can't see it being worth the risk. Although buying isn't a big risk. If someone scams you on your sale. You are SOL as eBay/Paypal almost always side with the buyer.