I think Larz gives some thoughtful opinions.
I like the front bumper style of the '08 Ms compared to the more boxy look of the '06-'07s and the "wavy" look that the '11 and up M37s have.
Many folks have done that mod to change the front end look of their older Ms.
However, there is an owner on another forum that has taken his M37 to a whole new level, there are some pics on the RavSpec website:
http://www.ravspec.com/archives/5715
I personally like the brushed aluminum interior trim, although some folks don't and others have even vinyl wrapped it or replaced it with their own darker aluminum trim themselves.
I love the low end torque of my V8 and the miniscule loss in mpg is worth it in my opinion, although no offense to my M35 brethren, the V6 is plenty powerful. Plus, all things considered the VQ engine may be a tad bit more reliable than the VK - I believe more have reported oil consumption issues with the V8 engine than the V6.
Although there are many of us that have NOT had any issues at all.
Plus, I think you get a 7-speed transmission with the M37 instead of a pretty antiquated 5-speed.
good luck with your hunt,
Craig