Do such meet ups mean anything though? If they're anything like those international affiliations of social democratic, liberal or conservative parties, then they're just useless talking shops who hold some annual convention, pass a bunch of meaningless resolutions that say "hey guys aren't our platforms the best? Yeah, we are so awesome!" and then adjourn and do nothing for a whole year.
Also I wouldn't call them as sold as the South African Communist Party. At least they support the party closer to their interests. The ANC went full neoliberal under Mbeki and is now effectively more anti-union than Scott Walker.
The SI used to be pretty active and did a lot of good work on détente and Israel-Palestine back in the day, having someone important and well-connected like Brandt in charge helped. They've rather faded since (joke leadership, lack of interest from the Europeans leading to dominance by the various dodgy Third World parties) and that weird Progressive (ugh) Alliance thing was, predictably, dead virtually from the start. I think the Liberal International still does a fair bit actually, particularly for parties just starting up.
I guess the main use of the far-left ones these days is as a useful shorthand for identifying the various sects. As for the parties themselves, well, Comrade Leader and his acolytes need a holiday every so often too and you might as well use those newspaper profits for
something.