There. You said it. They started the whole Wigga trend.. (No offense to any white MCs we might have here.. , but Beastie Boys provided inspiration to "posers" IMO..)
Yeah they sure have gone downhill since the heady days of whats the story? & definitely maybe.. but worthles is hardly the word, they're just not as good as they used to be. Same could be said about many bands really.
As for your second point. Lets not limit that to just white rappers. They all suck. Period
There are many bands far more worthless then the beaste boys. The police for one. Every single boyband targeted at young insecure romance believing girls is worse too.