absolutely worth it. the 960 is huge performance increase. even if you can just afford the gtx 950 its 100% worth saving for. the 750ti wont hold up well on new games.
GTX960 is significantly faster than 750Ti, but the price of a GTX960 is also way over priced comparing to GTX970 that's about only $50 more than 960. If budget is a consern, 750Ti or 950 both are good choices at below $100 and $125 respectively for 750ti and 950.
If you want high end performance at best return per dollar, GTX 970 or some AMD cards will run much faster than 960/950/750Ti .
I want to play games in my 1080p monitor 60fps with decent setting or max out which is even better. I don't like amd GPUs because I only have a 500w PSU which is not enough. This is the cheapest gtx 960 I found http://dynaquestpc.com/product/zotac-gtx-960-2gb-itx-128bit-ddr5-zt-90310-10m/, which cost 180$. Is zotac a good brand? Thanks for the answers BTW!