reliable, safe, smooth-riding, minimal maintenance, long-lasting car (sedan or suv) that won't cost an arm and a leg to own throughout the life of the car

I think the first question is, would your uncle the Volvo mechanic maintain your Volvo at a significant discount to the dealership and private party price for services? If yes, I'd consider getting one since, as you've noted, they're fun cars that just have the drawback of expensive maintenance. If no, you would need to ask yourself if the car is worth another $1k-2k per year to drive over more economical options. Maybe; maybe not.

The Mazda 3 and 6 offer good performance for their cost of ownership. You can get the "speed" version of either in order to get a turbo, but even the non-speed versions are generally a little faster than average. A relatively small percentage have leather, but they can be found.

An Acura TSX or TL would probably be the luxury cars that best fit your criteria. Not turbo, but good engines and better power/weight than your current car. Maybe an Infiniti G35 or G37.

Honestly, though, why not keep the Lexus? If you like the way it drives, rust is just rust. Are you looking for a car that drives well, or for a rust-free car to act as a totem of your success in life? Eventually an expensive repair will come along and kill the car, but until that day comes, it will remain your cheapest option you'd enjoy driving.

Volvos tend to require more repairs than the average car, and the earlier the model year the worse they tend to be.

Subarus are reliable for about six years, at which point they tend to take a turn for the worse.

The best cars for long-term durability are almost all Hondas and Toyotas. But I'm not sure how well they resist rust. And their reputation means they hold their value, so you'll have to buy an older one for a given amount of money.

The most luxurious Toyota is the Avalon. The first year of the third generation was the 2005, so I'd try to find one 2006 or newer. There are a few 2006s out there with leather and under 100,000 miles for your price, but not many. So it might be necessary to accept more miles.

Same for the Lexus ES, Acura TL, and Acura RL. The last has all-wheel-drive, so maybe it's the best of the bunch for you.