I haven't found SmartTVs to be a significant cost increase over the regular ones since last fall with the rise of <$1000 4k televisions. There are lots of premium TVs which heavily exhort their SmartTV capabilities, but comparing actual comparable models (size, panel quality, etc.) seems to be very little difference in price. Where there is a huge difference is getting larger, premium quality panels with superior color reproduction and refresh rates. Those ones are already going to cost a nice premium, and universally that halo market includes Smart functionality.
Let's go through a few specific statements:
1) "media-center computers and DVRs are ubiquitous" - Umm nope, not even close. They're common with middle and upper class white techy males and their families. Heck, I have XBMC on a PC hooked up to my TV and still use the native "SmartTV" functionality for Netflix and Prime because dealing with those on XBMC is extra steps and inferior. XBMC is for playing stuff I've downloaded almost exclusively.
2) "smartphones have HDMI connectivity" - Most do NOT, more have Miracast/AllShare or similar wireless tech. They literally overheat or lose battery while charging and mirroring whether wired or wirelessly.
3) "Raspberry Pi is inexpensive and can play 1080 content at full framerate" - This is a lot of extra work for non-technical common folk. You might have gotten more mileage from saying AppleTV, Roku, Chromecast, or FireTV. Of those, only AppleTV and Roku have a user interface and setup which isn't vastly more painful than the average SmartTV. Chromecast and FireTV are actually a huge PITA for non-techy people, and even as an IT engineer, I found FireTV to be a piling steam of slow crap, eclipsed in speed and usefulness by a $600 black Friday special (read: cheaper components) 4K SmartTV's native software (Tizen?). Further the $100 price tag for the AppleTV or better model Roku is more than the SmartTV price jumps in most situations.
4) None of these devices are terribly expensive anymore, and the price jump from a non-smart TV to a smart TV makes it difficult to justify the expense. - See original point.