I am also becoming less and less interested in such blunt in-your-face movies. Probably the toll of watching TNG-R (some of these typical mediocre 'let's do an allegory on XYZ' TNG scripts are really cringe-worthy).
District 9 does IMO only work because it is not just about preaching a message but mainly a get-thrown-into-the-action flick with some of this trashy charm of 80s flicks like RoboCop, They Live and so on. It is easy to do a Hollywood movie about whatever with this ugly condescending liberal distance, well-meaning as long as the poor subjugated folks do not come to close, there is ample of such crap on the market. But a movie win in which the protagonist is proletarized, becomes one of the very guys who is mistreated, is rare.
But of course you are right, District 9 is anything but a perfect movie and if we speak about proletarization, Moon was after all also about it but did it in a far superior way, without any melodrama. Furthermore cloning, biogenetics and so on is slightly more realistic form of being proletarized than becoming an alien.
Children of Men has shown that you can very well make a highly political and good science fiction movie when you put all of the political stuff into the background. Kinda like TOS which never (unnecessarily) signaled to the audience that it is sooo progressive with a Russian, a Japanese and a female Black officer.