^^^ I know exactly how you feel, I was just as wary before rooting mine. This is my first Android phone and I was pretty intimidated by the various rooting methods, ROMs, kernels, radio updates, etc.
First off, rooting itself does not necessarily require a wipe of your phone - I first tried with unrevoked3 and didn't lose anything ... I had a number of issues with "root only" apps not recognizing whatever unrevoked3 did, so I decided to go the OTA Simple Root route since I had the latest OTA update from Sprint, which does require a full wipe of the phone (apps, data, phone setup, etc).
If you've been using AppBrain it maintains a list of everything you have installed and as I understand it, should basically function as a backup since it will "sync" your phone with that list (i.e. re-install anything that is missing). One advantage to me trying unrevoked3 first is that I was able to boot into the custom recovery and do a Nandroid backup to my SD card (equivalent to a PC disc image), so I had that in my back pocket in case anything went wrong with the OTA Simple Root.
It helps if you think of rooting and custom ROMs as two separate steps - rooting just grants you admin access to everything on your phone which then enables you to do things like install custom ROMs ... basically custom flavors of the operating system.
This is the guide I used for the OTA Simple Root process:
[Program] SimpleRoot OTA 1.47.651.1 Edition - xda-developers
Make sure your PC has .NET Framework 4.0 and HTC Sync installed (links to both on that page), turn on USB Debugging, then download the Simple Root program itself and follow the instructions in the boxes that pop up as you hit each button.