Personally, I would leave it, but I love long manes ;)
My arab gelding's mane is near his shoulder and for the same reasons you were saying, I decided to braid it last week. However, after just a few days of being braided, my horse (who never rubbed his mane- hence why it is so long) was trying to rub it. The same thing happened to my mare, who also has a long mane. I decided that it was best just to leave it- I mean, that's how it got so long anyway.
ETA: And I am not referring to the horse in my avatar! That's my old man who only ever grew half a mane...I eventually trimmed it into a mohawk because it was so thin near his withers.