My brother and I recently did the timing belt, idlers, tensioner, water pump and thermostat (with associated gaskets for t'stat and pump) on his 02 Forester (I know, it's not an Outback...)
Once having everything apart, we noticed the following:
-- at 120k miles or so, the bearings in all the idlers and tensioner were shot. all sorts of noises were coming from them when spun by hand. they also had a lot of play in them.
-- the water pump gasket was essentially disintegrated and the water pump bolts were all loose...I removed them all by hand. water pump bearing made a lot of noise and had a lot of play in it as well.
-- car was purchased used at around 90k miles (by my brother) and had an unknown history. once we drained and refilled the coolant, we realized that the car was missing about a half a gallon of coolant (we removed 1 gallon and filled back up total with 1.5 gallons.) I have no idea how the car never overheated, but I largely attribute this to luck. upper radiator hose was bone dry and a bit rotten, so we replaced it.
My advice is largely anecdotal, but I would definitely replace all those bits while you're in there. Timing belt, idlers, tensioner, water pump, thermostat, all that good stuff. This was our first time ever doing this and it took us about 6 hours total, including coolant refill & burp (and a quick trip to the local auto parts place for a radiator hose.)