I bought this car after having looked at and researched many BMWs. My expenses have been minor. The previous owner had installed the optional 17" tires along with Eibach springs. This gave a great first impression (M5), but he didn't replace the OEM struts which weren't able to control the shorter more aggressive springs. I replaced the struts (myself) with Bilstein Sport units and the ride control was much improved. (Albeit a little harsh on rough roads.) I've put nearly 55,000 miles on the car since Oct 2003 and it going strong!
Styling. The 525i has a classic style that will look good for years, I get many compliments on the car.