Yes, I think it would help you immensely, providing you have the resources to buy the E90. If not, find the next coolest car in your budget and buy that one.
First and most importantly, driving the E90 with the BMW emblem, the feel of the car, the handling, the nimbleness, the exhilaration you get from behind the wheel-- will all lift your ego, self esteem, and confidence, which will boost your attractiveness. BMW is a lifestyle.
It is like wearing a fine suit or a fine watch. They honestly make you feel and look good, which makes you attractive, because you have confidence in your self.
Secondly, people like BMW's. I don't care what model you drive, 325, 330, 525, 530, etc.... it is a BMW. Even the people who make snide comments about BMW's like them. They just will not admit they like them. So, yes, girls, especially younger girls will like your car, it adds a touch of class.
Now, having said all of the above, the main factor is you, brother. If you portray an aura of confidence, are sincere, nice to everyone you meet, treat everyone with respect, help others, smile, give sincere compliments, and have or develop a good sense of humor, you will have all the chicks and friends you can handle.