Yeah, I think you're pretty much right. Lower level monsters will hit a bit less, thus the increased damage will mostly make things a bit more swingy but not a lot more dangerous on a per encounter basis.
I would tend to disagree. Swingy combats are more dangerous for the PCs, and when you add to that the fact that you'll be running more combats per level I think there could be a problem.
I don't think I like the update, but I don't think it's anything I'm going to get upset over. I haven't actually had a campaign get above 5th level, and the only thing that would really tend to bug me would be if lower-level encounters meant taking longer to level up. I think I may be less likely to go back to playing LFR, given the update, but that was already a situation where we had hard encounters vs. inexperienced players with (sometimes grossly) unoptimized characters.
As a DM I'm already reducing monsters' defenses, raising their attacks, revising damage (both up and down, depending on circumstances), and generally tweaking conditions. I also remove all but two or maybe three attacks from most monsters, just to make them readable / playable at the table. So I'm doing a lot of modifications, and while the update certainly doesn't help that, it's not really adding extra work either. Oh, and I'm not bothering with strict XP awards, so I don't have to worry about the levels dragging if I don't want to.
As a player I'm a bit more worried, but I still don't think it's going to be too terrible. We're leveling at a good pace right now, and while I don't really want to slow that down I don't think it's going to end up being a big problem. If the DM doesn't lower average encounter levels we could be in trouble. I dunno, maybe we'll pull through regardless. In any case, there have also been encounters that really weren't that much of a real challenge, but I don't expect that to change much.
My real concern is that I'm seeing spates of misses as far more of a concern than damage output. Like I said, I haven't played at Paragon or above yet, and if people are saying it's been an issue I'm quite willing to take their word for it. But I've definitely noticed that when you get a good number of misses / failures in a row (and I've had entire rounds where no-one, PC or NPC has hit with anything) it feels "grindy" in an immediate sense, even if overall the encounter is fun. Part of that is just luck, but I think that instituting a +2 / +3 overall accuracy boost has helped, at least in the game I DM.