Still dont see why they added LFD (at a greater than server level) in the first place.
Because the daily heroic functionality just didn't cut it.
On a bad day a level 80 dps toon has a 15 minute wait for an instance. It's allowed me to make ICC-ready a toon who came very late to the party. Admittedly I still ask in gchat if anyone wants to do a random, but I'm not hobbled if no one's up for it.
The explosion of lower-level instance runs has been astonishing. I have toons I never expected to see the inside of an instance. Now I literally choose which instances they do and don't go to.
There's a cost to community, I do agree, and I regret having to pay it. You meet some astonishingly mental players. Over the years there have been a small number of occasions when I've thought a player is so bad I wonder if I'm not the victim of a social experiment, and the new LFG system has made me think that more times in the last few months than I did in the years beforehand. I tried tanking pugs on a low-level paladin and despite enjoying the act of it, the players I met drove me back to dpsing. But the overall cost/benefit bottom line is well onto the benefit side.