Are you the original owner? Did you put most of those 50k miles on yourself?
Seems to me those are important points to consider because if you tend to consistently drive the car hard, then maybe an extended warranty makes sense.
As for me, I declined extended anything for two reasons:
1) Consumers Report, in an issue on car maintenance costs, noted that, out of all BMW models, the M3 cost the least to maintain.
2) I look at it like I am in a bet with BMW. And I don't like my odds. By that I mean, BMW is betting me 3k that my M3 will not cost me 3k to maintain for two years beyond my warranty period. Thing is, BMW knows the failure rate of every component of their car - I don't. I don't believe for a second "the house" would make that bet unless they were sure the odds were in their favor to come out on top