Dreadlocks are a common hairstyle in parts of Africa, as well as other places.  Leonard Howell who started the Ras Tafari movement in the 1930s didn't wear dreadlocks, and neither did any of his followers until later.  However, Howell was influenced by Indian mystics as there are many Hindu immigrants to Jamaica and Howell had also travelled quite a bit. 

Hindu mystics often wear their hair in dreadlocks, and in many depictions of Shiva, the god has dreadlocks.  Howell saw Rasta as a mystical movement as much as it was an pan-African one.  So, associating dreadlocks to Rasta came as the movement became a more mystical based movement, which happened in the late 40s through the 50s after the Rastas were evicted from Pinnacle.

However, most of my research shows that Rastas didn't start wearing dreadlocks until after the Mau Mau uprising in Kenya in the mid-50s.  The traditional hairstyle of the Mau Maus were dreadlocks, and in solidarity with the Mau Maus who were fighting to liberate their lands from British Colonial control, Rastas, and other Africanist groups started to wear dreadlocks.

Well, it is a spiritual thing as well.  Inasmuch as Rastafari is an Africanist movement, so the politics (within the relm of racial politics) and the spirituality are linked.

Like I said in my post, Howell was heavily influenced by Hindu mysticism.  This is directly where his promotion of Cannabis as a sacrament came from.  Hindu mystics often wear dreadlocks, and so did Nazarites (Samson and John the Baptist from the Bible), and therefore thinking of it as strictly a symbol of solidarity is inaccurate.

It is true that dreadlocks weren't worn by early Rastas, but the Rasta movement was rather small until the 50s when they started to wear them.

No.

My wife does.  She's had them for almost a decade.