First, there is no such thing as a perfect V70. Each of the 3 years you mention have faults and highlights. They are all 'old', this being 2010.

1998 was the last year for a single coil. 1999+ have coilovers which will crack and die at about 100K or so.

1998 was the last year for the hydraulic tensioner, but the Tbelt needs to be changed out every 70K miles. 1999+ have a manual tensioner which, with the Tbelt, get replaced every 105K miles.

1999 was the first year for VVT, which was supposed to help performance and mpg.

1998-2000 had problems with the vinyl pulling off the door pockets when parked in the sun. The only solution is to have the vinyl replaced at a shop that does upholstery work - but you need to take the door panels off.

1998+ the driver window switch is subject to rain/dirt accumulation, along with buttons that cannot take the heat and oils from fingers. They are a mess! Buying used is a crap shoot, new is around $100.

Only the driver's door has a key lock. So your remote(s) must work. Insist on 2 of them when you buy a car. It is dealer replacement only because of the programming and can cost over $250.

1998 was the last year for a non-chipped key (maybe 1999 also?), replacing a chipped key is quite expensive also.

1998 has evaporator problems - replacing the evap is like replacing the blower on the 240! 1999+ has a computer that will run the blower after engine shutdown to help the evap dry. All years have a cabin filter that must be replaced annually.

If you get an automatic, stick shifts are rare, check the tranny fluid. If it is a 5 speed, it requires 3309 ATF also carried at Toyota for a cheaper price than Volvo. The tranny should be flushed every 50K miles, unless you are a road warrior on the Interstates, then I would go for every 4-5 years.

Any V70 you buy will have pluses and minuses, including the 2007. Lower maintenance costs for the 1998 because of fewer computer controlled things in the cabin.
All Volvos need to have the PCV replaced at 150K miles or 10 years. Engine mounts tend to fall apart at the 10 year mark also.

Look carefully, and maintenance records are worth at least $1,000. Deduct that much if not available. Dealer maintained means nothing because dealers only replace parts, they do not do preventative maintenance. I would rather buy a car with 150K miles with records than the same car with 70K miles and no history.

Have fun looking,

Klaus
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Praying for Cynthia Amendt, heaven bound