I tried to unlock the bootloader at HTCdev yesterday and didn't have any luck. I've rooted two phones and four tablets using adb so it's not like I'm a complete noob doing this. You will need the Android SDK and Java Development Kit installed. Was never able to figure out the error I kept getting which is really annoying because I had to update my hboot by installing the 2.2.2 RUU. Rooted my phone (Android 2.1) early last year using Unrevoked but it was still S-on. If you can get it to work at HTCdev great, if not you can use
Revolutionary like I did. If you use Revolutionary it's best to copy/paste the alphanumeric serial and key, some characters don't display right (l&1). After you unlock the bootloader you could just go to the market and install the superuser apk (binary?) but you should seriously consider at least installing Clockworkmod Recovery. That way you can make a backup (nandroid) of your system as it is now. If you were to install Titanium and do a backup with that you could choose to restore any app and/or app data if ever needed. No, you do not need to install a custom rom but if you did it would have the superuser app, binary and busybox. I'm using
Liberated Aria 2.2.2 which is an optimized version of the stock HTC Aria AT&T Android 2.2.2 ROM. Everything works including trackpad wake, ability to overclock, sideload apps, wifi/usb tethering and you can probably flash over what you have now (wipe cache and dalvik in recovery first) but I would do a factory reset. You can remove the bloatware but using a rom gives you an easy way to update all the google apps (inside the rom) and any other app in the system. All the system app updates steal a lot of storage. From what I've read keeping at least 20MB storage open makes a big difference in performance, I personally don't know, never had that problem!
If you decide to try Liberated 2.2.2, I could upload my copy that has updated apps, hosts file, gps.conf, Android 4.0 fonts. Very long story short, unlock bootloader, install superuser, go for it! Good luck!