Rooting is useful for sure but you will void your warranty. However unrooting and reseting every thing to stock will give you warranty because no one will know that device was rooted or not. Rooting will give you ability to install custom ROMs that have different taste than stock. These ROMs increase performace, battery life etc. Only root doesn't improves your performance, it gives you permission to edit anything in system. Some root apps can improve performance for you, more performance can be achieved by custom kernel because some of them have ability to overclock CPU and GPU. I have S3 with stock ROM and custom kernel, I can overclock it from 1.4 Ghz (stock frequency) to 1.6 - 1.7 Ghz (OC), but I don't do it because it uses more battery.. Overclock might cause instability but if it is stable, it will increase performance. You can get more free RAM by apps like "greenify", it can hibernate select user+system apps to free up RAM + less load on CPU because apps have its process too. Rooting can also give you ability to change boot animations, change status bar style, theme system apps etc. But if you are happy with it as it as, leave it unroot till it lags/ get worse on performance/you get bored by it/ warranty is over.
Btw you have good device.
EDIT: You can use some game cheats, like CLEO that gives you cheats for GTA 3, vice city, san andreas.