Since you have mentioned you want more performance than your current bike, you should look at the Royal Enfield Hunter 350 and TVS Ronin, as the Yamaha FZ will only offer you a very small step up in terms of sheer speed, although it will offer you vastly more fuel efficiency in the process.
Take a test ride of the Hunter and Ronin before you decide to go ahead with your purchase.
Coming to what price you should sell your bike for, there are a lot of regional factors that come into play, as well as the market rate of your machine. We would recommend speaking to a pre-owned bike dealer in addition to putting some feelers out in the market in your individual capacity to get an accurate picture.