Spot is correct. The backup file only restores your personal information, such as contacts, emails present at the time of the backup, BBM contacts, etc.
Posted from my CrackBerry at wapforums.crackberry.com
No. Wiping is mostly about preference. You definitely do not "have" to. Technically the DM does the same thing, but just doesn't always do it as well as JL_Cmder. If you aren't very experienced with your device, hold off on the wiping, and just upgrade.