Well, just to show how relative the title of "Best Car Ever" is. My "Best Car Ever" goes to the 2002 Porsche 911 GT2. Luggage space is a very nominal thing to me. I also dont like the idea of one car trying to juggle a whole bunch of categories at once. I would rather buy a 911 GT2 becaue 98.9% of the time I am just commuting or driving with a friend with mostly NO luggage or crap with me. If I HAD to go for some long distance trip and I needed luggage space and room for people, even if my $100,000+ car could hold luggage and people I wouldn't want to take it anywhere hauling people and things. I would sooner buy a 1990 Civic 4 door for a trip than take my expensive car all over hell.
So, basically, if I had an M5 which is capable of all that, I STILL wouldn't want to use it for both sides of the spectrum. So why buy it because it can do 2 things pretty well, when I can buy 1 car that can do the thing I do 99% of the time EXTREMELY well. i.e. 911 GT2. The price of a 1990 Civic Sedan would be less than 1-2 options on a GT2 or M5. Have you ever looked at the options list for a 911 Turbo. I believe chrome treatment to the door sill's is a $500 option and a leather wrapped console is a $400 option.