For something like this
http://www.carsales.com.au/dealer/details/Volvo-S60-2011/OAG-AD-13974392/?Cr=1
In general very reliable and no real gotcha's on the car
Theres nothing special on them that is highly unreliable or stupidly expensive
The EGR will likely clog at about the 7year/120k point... but its easily cleaned out with some carb cleaner and re-fitted and good to go for another 7years/120ks
Volvo for various reasons says you dont need to do half the service you really need to do so budget for
-TIming belt is every 8 years 140k (volvo says more but mehh)
-Oil = Penrite HPR10 10w50 oil
-Change of haldex unit fluid and filter every 5 years or 100k (would be due now)
-Change of angle gear fluid every 5 years or 100k (would be due now)
-Change of rear diff fluid every 5 years or 100k (would be due now)
-Flush trans every 5 years or 100k (would be due now)
-Change fuel filter every 1 year or 20k (would be due now)
The above which would be due now is about $1k in work and parts so just factor it in to any purchasing thoughts
As the car is out of warrenty, a number of (much better than polestar) tuning options are available
That said... the factory output is within 10% of the max torque rating of the Transmission so there is very very little to be gained without considerable risk