I ended up buying a matched soundbar from the same vendor (Panasonic Viera), one that uses HDMI and connects to the ARC-enabled port on the TV, which means basically all three gizmos (HTPC+CEC running XBMC, TV and soundbar) can be controlled with just the TV remote. It also means if I turn off the TV and just use the HTPC/XBMC + soundbar for music, the xbmc mobile app can control the speaker volume.
It's all basically as straightforward and usable as it can get. If I were going to buy a Smart TV again I might get a Samsung or Vizio, as there's a Plex app available for both. Which is a whole nother topic. (I don't use Plex myself but it's what I'd recommend to pretty much anyone I didn't recommend Apple TV to, i.e. someone who doesn't have a houseful of predominantly Apple goodies already.)
I avoided the price-attractive Vizio after reading a large number of reviews of later models that suffer from persistent random reboot issues. No point in a smart TV that can't be a TV reliably IMO. The picture on my Father-in-Law's Samsung (dumb) TV is outstanding.
I went Sony only because I have a good experience with Sony products, their tech support was rated higher than everyone else's and they offer four HDMI inputs to everyone else's two. It seemed to me that I'd be bunging wires into it from all over the place and better to find I had too many sockets than too few. I'm also familiar with the Sony video family "quirks" and it seemed likely I would have a better time getting the clown out of the picture.
I think it's better to go with the direct-connected HTPC because transcode-network-decode-display is a lot more bother than just decode-display; but not having a HTPC would be attractive if your Smart TV was actually smart enough to do everything you want, and playing local media in whatever format is a major sticking point.
Yesterday he was being interviewed on NPR as I was driving home and the interviewer asked about the difference between what people, upon recognizing him, were likely to shout to him in America as opposed to the UK.
His answer was interesting but too long to go into here. It did, however, include a snippet that might allow for much japing should one of us encounter the great man in the future.
He said that often, people would make reference to sketches that he couldn't remember participating in, and he would just smile and nod and say something neutrally agreeable to fake it.
So the next time you see John Cleese, get close, make yourself known (this may involve acting as I know none of you would never slip into nudge-nudge, wink-wink territory normally, being too cool for that nonsense, but the payoff for doing so will, er, pay off) and say something like: "What about that time you were the astronaut lost among the vikings, who all turned out to be women? Talk about funny! I only saw it on DVD, and they blanked the punchline. What was it you said right at the end there, when "Mrs" Eric the Viking Idle showed you "her" buttocks and demanded an autograph?"
Also, to minimize the risk of vigorous shoe-licking instead of ankle-nipping, thrash the dog soundly for five minutes a day with a side of bacon.