Well, I don't think it is considered an optional procedure. Also, the recommended timing belt change for a 98 is 60,000 miles. It is 90,000 miles for my 2001.
The 3.4 V6 is considered a non-interference engine, meaning you won't destroy the engine if it breaks. I lot of members seem to go well past the 60 or 90,000 miles and the belt has not broken. I have decided to go to 120,000 with my vehicle before I change it. I now have 102,000 miles and my Son will probably get it by then. I will change the belt before I give it to him.
Your car is older, but with less miles. I have read of some going over 160,000 miles, but I would think I would change it by 120,000 miles with the understanding that it could break at anytime and you will be pretty much stuck. If you are on a vacation, that would pretty much suck, big time. Planning for a belt change could be cheaper than an unexpected belt change.