Are you 100% sure that the lumpy feeling and the vibration are related? I mean - the vibration could very well be drivetrain related. Maybe you should have a look into that as well as engine mounts like mentioned above, etc.
Otherwise, it oculd be as simple as a full tune up - or something like sticking injectors, vacuum leaks, etc.
If in the rare event this car had a more serious problem, I don't possibly see how you could be skeptical of buying another BMW in the future - You got 230k miles out of it, thats well past the typical life expectancy of any car on the road. Sure, we can all keep our cars running past 230k, but at some point you have to realize the car isn't what it used to be and it's not the car's fault. lol