From the prophet:
من سن سنة حسنة فله أجرها وأجر من عمل بها إلى يوم القيامة
Whoever who creates a good tradition, then for him is a reward. He is
continuously rewarded for whoever who follows till the judgement day.
This is talking about NEW things. Similarly if it's bad the person is punished for everyone who follows.
So if a person lays down a tradition that Muslims gather for the prophet's birthday and then people read some Qur'an, stories about his ethics, or his narrations, read some poetry about the prophets, have a program for the kids and give them gifts so the kids remember its significance then why not do this?
However if Muslims used this occasion to sing and dance and do nothing that reminds them of the judgement day then it's a bad tradition.
My point is it being done before or not isn't important as long as it's not haram.
Adding a march to all this can be considered as a way to honor Prophet Muhammad somewhat differently. I've met Christians who are curious for our traditions. Perhaps such marchs can be used as a medium. That being said if the marchs are just used for Muslims to come and have some and hear some Music then there isn't much benefit to it. All in all these 'cultural' or 'modern' activities are OK as long as they are heading towards something haram. Forcing cultural mindsets on other Muslims isn't right. Saying something non-haram is haram is wrong just as much as saying something haram is non-haram. It's not like if someone is asking can I touch a non-mahram or not. That's haram. That's cultural. But this march can have different motivations and is treated differently in different countries.