Is anyone else worried about this "mystery" illness that has been spreading around in dogs?

No sense borrowing trouble by worrying until there is a clear plan of action to take to protect your dogs. Keep your eye on it, but otherwise you've got to live your life.
Guess you're right about that. I just hope that whatever it is won't come down my way, at least not until proper protection has been developed against it.
There's an article about it here:

Apparently vets are saying not to push the panic button quite yet, but I still am concerned for the safety of my dogs.
just make sure your dog has their flu vaccine up to date and you should be ok. avoid dog parks, daycares, etc where you might run into contagious or asymptomatic dogs.
Did a little digging and it does look like int the past year there's a few reports of cases popping up here and there of dogs with "kennel cough" like symptoms lasting longer then expected, with a few turning into more serious pneumonia. Testing for common respiratory disease agents has come up negative, and the causative agent has not been clearly identified. The U of New Hampshire seems to have suspicions on difficult to culture bacteria, which doesn't respond to the usual first line antibiotics for pneumonia. It didn't sound like there as a very high number of these cases. The news makes it sound scarier then it needs to be.

If you're worried for your dogs, basic precautions against contagious respiratory diseases is the most obvious thing you can do (avoid high-traffic dog areas and dogs of unknown health status).
Vet here, dealing with this in clinics right now. All good advice here—I’d add to get your dogs updated/boosted on canine influenza vaccines and Bordatella until we figure out exactly the etiology of this bug. Usually the really bad pneumonias are caused by a blend of infectious causes that include those two—protection against them goes a long way.
Well, never heard about it until now.

Really, given the simptoms, timing, and human-dog proximity, a Covid variant jumping species is not too far fetched as hipotesis, as well as a more aggresive mutation from the usual kennel cough, but I guess that would more or less react to the usual treatement.

Has anyone, out of curiosity, done an standart Covid PCR to some of the affected animals?
(Even if it might not even be able to mark it any more)
Taking my humble vet opinion with a grain of salt—I’m no epidemiologist—Canine infectious respiratory disease is always a thing, and I deal with it every year. To be honest, I don’t have any idea if the current media stories reflect:
  • A multistate outbreak caused by some new bacterium/virus
  • A multistate outbreak caused by our usual suspects, for some reason
  • Unconnected sporadic local outbreaks caused by usual suspects
  • A slight increase in baseline disease
  • Our normal disease activity with an outbreak of media attention.
I suspect it’s one of the last two. Lots of media attention for respiratory diseases because of COVID and all recent concerns, so that you look at your dog sneezing and rush them to the vet rather than just ignoring it.

Don’t get me wrong, I will always appreciate more people giving their puppers better healthcare, but this I really don’t suspect a major new disease.
The part about not responding to the usualtrestenentsis, to me, the most meaningfull of something new.

But, you are totally right. News hype will make about impossible to know IF that is a fact or just some isolated normal cases being shown as alarm signs.

In any case, and while there is nothing sure, be careful and keep life going. No gain in panicking
In a way, a pity. It would have been relatively easy to test human vaccine and approve them for animal use.

Upper vias... I suspect there will be some public mass hysteria at any outbreak of standard kennel coughs?