I wouldn't worry about it unless you have a locker in the front axle. The YJ has a very strong boxed frame and is not known to break around the steering box under most wheelin conditions. I have a lincoln locker in the front of my '95 YJ, which is a LOT of stress on the steering system when offroad, and have had no problems without a brace.
Spend the money and time where it's needed more.