Crap -- I forgot about Ent. Hmmm... maybe that an argument that Ent is a alternate future created by First Contact / pick your own point and reason of divergence. And so did the Phoenix in First Contact as I recall.
Or maybe it is purely cosmetic, just a little bit of bling chosen by starfleet as sort of an identifying beacon. Then warp really just looks like it did in TOS, with no particular light or streak effect, and these things are just added. Different styles of flashes and streaks go in and out of style depending on the era. Which could make sense if, you want to have a way to quickly identify yourself as soon as you enter or leave a sector.