According to mileage you don't need it. However there is a lot to be said about preventative maintenance. Most people take the attitude "if it's not broke don't fix it". Not necessarily the best thing when it comes to your car. The belts on a car are made of rubber material and do get dried out an cracked. Being it's been 10 years it wouldn't hurt to do it now and avoid it potentially breaking and having other problems. There's no real way to say if you NEED it. It would simple be a recommendation for preventative maintenance. It could last you 3 years or 3 weeks....there just know way to know. You really have to decide what is going to give you piece of mind. If it's in your budget and you do it now it would be off your mind for another 10 years.
I am with Bret on this one I have an S80 w/191000 miles on it and have replaced the belt three times, the first was due to a failure of the tension spring. While the car still ran I was cautioned that if this happens and the belt breaks or slips it is very possible to bend a valve or damage a piston or the head. I will drive this car till it dies and I will change the belt and tension pully every 75 - 85000 miles.
The timing belt would likely be OK until 105,000 miles, but the timing belt tensioner will definitely not last that long. I've seen some of these tensioners go before the 105,000 mile interval, so I wouldn't push it. While your having the belt and tensioner replaced, have the water pump and idler pulleys done as well.
Bretb, You seem to know the 2000 Volvo S80 non turbo, well. Today at 162,000 my timing belt just died while I was out on open road - so having just towed it, I am now in rental car mode, who knows how much engine repair/damage will be, cost. I want to support your dont push it answer for anybody who reads this - Just Go ahead and change it while your in your shop/not on the road in a strangers hands.