Not familiar with the Milan at all, but assuming that your E46 has been lovingly cared for so far, it ought to be a maintainable automobile for another 50-100K miles or more.

Find yourself a trustworthy independant mechanic who can/will fix Bimmers and run that one until the wheels fall off or you finally get bored with her.

That would be my advice. I regularly drive an E39 540i and now an X3 and I still really miss my lil' old E30 325is.

Good luck with the decision.

D