Dr-RS

I'm starting to look at buying a 640d m sport convertible to replace my E93 which I have been using as a daily but I will soon be retiring and I would like to do it in a bit more style. A local dealer has a 2012 Pre LCI and 2016 LCI in stock 40,000 miles vs 20,000 miles and £20k vs £30k. My questions are: 1). What is the difference in spec between the two. Is it just a cosmetic facelift or are there mechanical differences? I see the LCI gets a digital dash, what else was there? 2). There is massive early depreciation, how much does that slow down on Pre LCI cars? 3). What are the desirable extras to have? I've read adaptive drive, variable damper control, driving assistant plus, comfort seats head up display and harman kardon are all nice although the first four are quite rare. What was included in the M Sport Plus package? 4). What are the common faults to look out for? My E93 is getting on a bit so I'm paranoid about timing chains and roof failures. How reliable is the F12 roof? Any advice gratefully received. Thanks in anticipation, Keith.