In my limited understanding, kernel upgrade is really not required and Nvidia official drivers could be updated without a kernel upgrade.http://www.upubuntu.com/2012/10/install-nvidia-driver-31014-on-ubuntu.html
Although I have installed kernel 3.8 (for Fun + Experimentation) following this
link. Some caution - I did face some issues and had to uninstall Nvidia drivers to go ahead with kernal upgrade. I am yet to get the Nvidia drivers working under bumblebee. (Have Nvidia 540M graphics Optimus card as secondary video card). So am yet to play TF2 in steam on the new 3.8 kernel. I will update here - guess it requires some re-installing of bumblebee , nvidia drivers, etc.
If everything is working fine and you're getting satisfactory performance on Steam games with your current driver setup, perhaps you're better off not upgrading.
Nvidia-current gets automatically updated after it becomes stable? Not sure...