So where a 530d MSport may have cost around £35k 8-10 years ago, it is now a £50k motor. So the depreciation starts at £50k, not £35k, so in 4 years, it's no wonder it's not down to £10 - 12k.
This isn't really true at all. The 5 Series hasn't really increased in price that much at all, infact in real terms its probably cheaper.
We'll start with your £50k figure - its nothing like that. It lists at £43k and Broadspeed will set you up with a main dealer supplied 530d M Sport for £36k.
Now lets look at the price of a 530i/528i or similar across the last 15 years.
2001: 530i Sport, 231bhp with leather, Xenons and navigation was £38k list price. Discounts were not as significant back then but lets assume 10%.
So a 530i Sport with those options would have cost you £34k or so 13 years ago. Adjusted for inflation, in 2012 money thats.. £48k! To be honest thats optimistic too, I have the original purchase invoice for mine which has no navigation and that was £32k inc discounts.
So lets assume you want the same today. A 230ish bhp petrol 5 Series M Sport with leather, Xenons and nav.
Accoridng to you, loads more money.
In reality, a 528i M Sport with 245bhp, leather, Xenons and navigation is yours for a LIST price of £38k but a discounted price of £32k.
It has likely never been cheaper to buy a new 5 Series as it is right now.
Something else is holding F10 residual values up - they are IMHO crazy high. You want a decent 4 year old 530d F10 with good spec etc? You need at least £20k. For a 4 year old car! You want a 2012 M Sport? You'll need almost £30k for a car I've demonstrated you could order brand new right now for £36k!
They are really bonkers expensive, especially compared to the equivilent E Class or A6 which is generally noticeably cheaper.
It's really quite annoying for those of us who don't buy new cars but really rather good for those who bought a new one 2-3 years ago!