Yes mate. It needs changing. I changed my cambelt few days ago and I think the engine runs much smoother.
To justify my answer: basically a new belt will put a swlightly(if not significant) more pressure(tension) on the tensioner and the other components moved by the timing belt. More stress(pressure) on some worn parts could lead to their failure which could cause some really expensive damage to your pocket and your engine(or the other way around :)). Is something similar with changing the oil...is not compulsory to change the oil filter but you don't want fresh oil to run through a dirty oil filter. So basically this is the reason why you need to change the tensioner and the idler...just for your peace of mind. You will not get in there for the next 100.000 km so I don't think the old tensioner and idler will last that long.
I am a bit crazy if i say that I chnaged the oil seals for cams and the waterpump. Nothing wrong with them but i just wanted to make sure everything is new in there.
On the other hand though, when you sell the car, mentioning that you replaced such and such with new parts, could put some extra money back into your pocket, if you know what I mean. That shows to the new owner that you looked after it and you didn't cut any corners.
Good luck.
PS. I am still amazed by how smooth an engine could run after the belt has been changed. The guy might've fixed the timing on my car but now I am happy again. :))