Ron:

Turbo upkeep adds some maintenance to the equation, but it's not prohibitive, in my opinion. Synthetic oil would be a good idea, though.

AW71: A very durable automatic. Typically only troublesome when abused for a long time.

Service Light: No problem. Oil change reminder. Reset button.

Worn Turbo Check: Pull off the air hose at the end of the shaft, and wiggle the turbo shaft. If it has excess play, it likely will soon need attention. If so, it can, however, be rebuilt for a reasonable cost (I paid about $300 US for a rebuild in the States.).

Running without boost: Probably not.

Premium fuel: Not required.

Gas mileage: About 10% less than an NA.

Hope this helps. As always, you might want an independent Volvo mechanic to check it out, just to rule out any big headaches before purchasing.

Best of luck in your decision.