It was a key moment - another major steeping stone in the growth of the movement.
Before that:
The bombing of North Vietnam in '65? seemed to get things really rolling
Bob Dylan and Joan Baez helped the music scene and artists get involved using non-news media and concerts to get the message out
MLK (who showed students the ropes on how to protest the war) & other civil rights leaders came out against the war.
So did RFK and others.
Walter Cronkite coming out against the war in early '68 was BIG in terms of gathering support in the media and from the more conservative public.
The protests in DC, NY & CA and elsewhere along the way grew larger and attracted more media support as the crowds grew. It was too big for the media to ignore.
Other artists, musicians, entertainers got on board. etc
The assassinations of MLK & RFK earlier in '68 stoked the unrest further
So the '68 convention was another key event in a string of events that helped get more media and citizens on board. At that juncture though, I'd say the momentum of the movement was too enormous to be denied.
After the '68 convention, the slaughter of protesting students at Kent State by the National Guard in the spring of '70 was another big moment we might relate to Ferguson to remind ourselves of the real and present danger the citizens of Ferguson are in right now. And for those wringing their hands over getting justice for Mike Brown, the families of those Kent State kids are still looking for the truth of what happened there today.