I recently went through the same considerations you are going through. Just traded in my '99 V70 GLT for an S80 T6. I really enjoyed driving the V70 and seriously considered purchasing a 2002 V70. I average 32,000 km per year and the V70 had 104,000 km on it. No problems over the past 3 years. Change the oil & filter every 6000 km and service every 12,000 km.
The S80 is great to drive, lots of power. The seats are very comfortable, with plenty of space in the rear seat, too. I'm 6'3". One of the initial reservations I had was cargo space. The V70 has lots. However, the S80 has a large trunk. I decided I didn't need the space a wagon provides, as I didn't use it all the time. It was just nice to have. I first found the S80 almost too smooth and quiet. The V70 had a more solid, firm ride and the steering was stiffer. Although I find the S80 steering light, I'm adjusting to the drive and I really enjoy it. The S80 is a great car. Before making my final decision I checked into the 2001 & 2002 S80's and found that the problems the '99 model had were basically corrected in 2000 and 2001. It's too soon to know yet but I think I made the right choice. I know I like the car.

M.Mc.