The question is: how good do you need/want to hear your music while you're on the move? Assuming that that implies being concentrated on doing something else, too.
IMO you only need serious hi-fi (meaning it's only worth the effort and money) when you have the pleasure and freedom of devoting yourself entirely to music listening.
I speak from personal experience, BTW. When I'm out at the university, I hardly even have the will to bring out my Creative Zen Mozaic + Senn MX460 and have a listen.
And even when I feel like listening in some pause between other activities, the quality produced by that setup feels quite satisfactory, unlike what would be at home, where I rigorously keep my portable
(and even modified to make them better) portable amps, besides the better phones of course.