Yacov Menashe Ben Rachamim , i can surely tell you that the fast thing is extremely unpopular by other Ethiopian communities here, although the "ghetto" environment is. i live in the Kerayot, just north of Haifa, and its very prominent here. every black kid dresses like the "brothers" from the US, these over sized shirts, the rap crap music, they even spray names of rappers on walls here. i would define their children's way of life as "wild" as they cause damage on the streets, beat up cats (i always act against them when i see it) and stuff like that. however, the elders seem to be very rational, extremely polite, the youth goes to elite army units, and they are very devoted to the country and to how they see Judaism.
They have been so separated from the Babylon and the Jerusalem Jewish communities (which made all the halacha as you know) that they developed some of their own "halacha", which as you noted contradicts the main one in some cases.
I believe they need some more time to adapt to Israeli way of living, and i guess they would change some of their ways of worship, although i dont know enough to judge their fasts or other deviations from halacha. I surely believe they must stay here, and we must help them develop in the right way- thats my opinion anyway.