Oh there is SOOOOOO much more to rooting than just performance tweaks! Which include MORE than overclocking & roms! These developers can do AMAZING things with Android that iOS fanboys can only DREAM OF! BUT they do need an open platform to do it on. even if you feel overclocking is not needed there are battery tweaks, screen tweaks, and various "hidden" performance tweaks that I don't feel like writing at the moment. BUT there are also COSMETIC tweaks that you CAN'T to on a stock rom...changing the navigation bar buttons to what you want, status bar tweaks including (but not limited to) weather in your status bar, full access to major settings such as wifi, bluetooth, tether, GPS, LTE, etc....Lockscreen tweaks such as adding/changing the apps on the lockscreen, battery % on lockscreen, torch, different wallpaper than your homescreen, etc...modifying the build.prop file for performance & cosmetic tweaks...
The performance tweaks alone are worth rooting...but with the cosmetic tweaks you can REALLY make your phone your own! Rooting is a choice...either you want it or you don't...but research is your friend. The nexus has it's doors open...it's NOT perfect. As of this day ALL phones/technology have some faults. However rooting helps to fix some of them
And not to burst anyone's bubble but Moto WILL hold ICS even longer! Trust me...us former & current Bionic users feel completely cheated by them!