I'm a little surprised that you didn't mention any of Cantet previous three films: Time Out, Human Resources and Les Sanguinaires. (The obvious reason would be that you simply haven't seen them, though that'd also be a surprise.)
I agree with you. It's a good, ambitious film which perhaps tries to tackle a few too many issues, but that's certainly preferable than suffering through yet another safe, middle-brow affair.
Heading South was adapted from three short stories by Haitian-Canadian writer Dany Laferrire, which might be the cause of a certain unevenness in the script. But it starts strongly, with Cantet meticulously mapping out the emotional, physical, and psychological terrain. The way he showcases the bodies with all the desires they embody is almost Denis-like (who probably could've made a masterpiece from this material).
"Although the film doesn't cover the political climate to any major degree, that isn't really its intention anyway."
You're right, local politics initially did remain in the background. Though they did play a role in the film's final, somewhat conventional thrid act. (Cantet made his point earlier, and quite poignantly so, by not allowing Legba to have a "say," unlike the trio of white woman and the black restaurant owner.)
"The way the women use the local boys seems almost acceptable, yet if the position was reversed, middle aged men with young girls it would rightly cause an outcry, though of course unfortunately it does happen in a few parts of the world."
You mean locally (the outcry, that is)? Either way, black or white, men or women, it's always the poor who get taken advantage of.
"The performances are all very good as you would expect from the older cast, theres also a great first time showing from Mnothy Cesar as Legba."