If it's due to be changed do it.
Once the mechanic has the engine all apart you might as well have him change the timing belt while he's in there cause there's 5-7 hours of labour involved. Have him check the water pump and other belts at the same time and replace that too if needed, they can be done all at same time and save you some labour charges down the road.
I just got my timing belt, waterpump (was leaking) and a couple of belts (alternator,power steering belt and belt tensioner) changed at 109,000 km and it cost me about 7.5 hrs of labour (labour=$450 cdn. @ $59/hr) Job cost me around $1100 cdn parts and labour at my local trustworthy mechanic.
It's a big job but will last about 5 years give or take. (60,000 miles or 100,000 km).