I am at 100K with my X3 and currently also own a 330xi. Granted both are 2004 so there are some differences in what you are looking at, but for the majority not much. I have spent more time and money on the X3 than any of the 20 vehicles I have owned in the past, including 3 BMWs. at 100K I had to do AC compressor, coolant system, dealt with electrical issues, new switches, broken suspension spring, I've had to do all fluids which unless you are a rocket scientist you'll never know what type of transmission fluid to put in the auto transmission. Took me six months to finally make an educated guess. I've had to replace manifold gasket, valve cover gasket, leaking intake boot, and oil filter housing gasket. This is all I can think of off the top of my head. Maintenance has seemed to be the exact same as the 3 series I've owned in the past, in fact a bit more, but the X has a little more fancy stupid stuff which has added to the list.
I get 24mpg highway and 17 city. The ride is harsh and stiff. Handles like a 3 series car, but a little bit taller. Interior looks and feels like a 3 series car, again just a bit taller. The rear leg room is lacking. Tried to put 2 adults back there this past weekend and they very kindly said they were fine, but it was tight. I can fit the dog in the back which is great and so far has been the only reason I love driving it. The automatic transmission even with the manual shift option has a mind of its own and the delay between what my mind and body do and what the car does is so long its a joke.
I love driving my manual 330 far more than the X. The ride is the same, but its far more fun. Unless I've got the dog. From a fellow BMW enthusiast and long time owner, I would recommend looking at a japanese SUV. Unless you just want a bigger 330.