The values are certainly dropping!!
Having owned a E60 M5, F10 535d and now a F10 M5 I can offer an insight.
The E60. Great car and a cool sound. In the end the SMG wears you down though around town. I also have a E46 M3 CSL and the CSL box is a lot worse, but on track it's great. Fuel wise I saw 17l per 100km on average.
The F10 535d was very good but boring. I liked it at first, but when the F10 M5 came out and I drove it I knew the 535d ownership would be short.
The F10 M5 is truly fantastic. To put it in perspective in the last 4 weeks I have probably driven 3-4,000 Km in it between Akl, Napier and Wellington. It is a great open road cruiser and a seriously fast car when required.
The F10 M5 is the best 4 door "sports" sedan out there I think. Fuel wise I see about 12l per 100km on average.
I do actually miss the E60 though. It was fun and the noise of the V10 at high revs was pure goodness.
At 40-50k the E60 make a lot of sense. The SMG will be OK if serviced well etc. remember these are built for huge mileage in Europe where 100km/60miles is nothing.
Now - I must head out and give the F10 M5 a spanking.