If all you want to do is overclock - no. Just flash giantpune's kernel through ClockWorkMod, and you'll be good to go. However, there are nigh-innumerable advantages to having a custom ROM, in addition to a simple kernel change (which is what allows you to overclock - a custom kernel). Simply overclocking helps the phone a little bit, but other changes made in custom ROMs such as changing the dalvik vm heapsize, etc., can impact gaming and overall smoothness largely - and these are done through various methods (editing the build.prop, init.d scripts, etc.).
As such, with numerous other behind-the-scenes improvements (especially concerning battery life, potentially up to 60 or more hours as opposed to an average of 12 for this device is quite appealing), there is little reason to
not format a custom ROM, but to each their own of course. A good ROM doesn't alter your data, or what you're doing, it just improves how Android handles all of what you're doing, making it more efficient, and more capable, and, ideally, consuming less energy to perform what you tell it to - but being able to perform everything you tell it to, and more if need be.
If you were to flash either a custom kernel (like giantpune's), or a ROM, you will not lose your data unless you yourself intentionally format/erase your data.
As far as any worries go about bricking your device, for all foreseeable things that you would do to your device you do not need to worry about bricking it - make a Nandroid backup before you make any changes, and if one of those changes bricks the phone, reboot into recovery and restore from your Nandroid backup and you'll be back on your feet in no time.
For the LG Optimus Elite, all of this and more is documented in noob-friendly syntax at the following URL:
http://androidforums.com/elite-all-things-root/620742-faq-guide-clockworkmod-optimus-elite.html
I second that. All of it, in fact.