If you're a capable mechanic and can do most of the work yourself, then the 960's/S90's are nice cars that won't cost you too much.

If you have to rely on a mechanic to do even the basic stuff of brakes, timing belt, struts & shocks and that sort of thing, then these cars can get rather pricey to own.

You must do pro-active maintenance on the engine/cooling system to make absolutely sure that you never have a cooling problem or a timing belt failure. If you have one of these, it will cost you big time. All the components in the timing belt area except the pulleys must be changed out at 100-140k miles for insurance against this sort of thing. This will set you back ~$500 for the parts.

Then there's the plastic car syndrome with lots of motors and electrical things to go wrong. These things are less disastrous, but still expensive to fix if you don't fix things yourself. Even if you do fix things yourself, these cars will not be as cheap to own as an iron block 4 cyl like your 740, so be prepared for that.

After all that warning, I'll say that I love this motor design. The rear wheel drive version has a very friendly layout in the engine compartment that is fairly easy to work on.

I have two 960 wagons, both the same year and do all of the work on them.