Yeah, in my mind SeÃ¡n it follows the laws of diminishing return.
DVD was a massive leap from VHS and almost everyone followed.
Blu-ray is better than DVD but you need a decent TV and a home theatre system to really reap the benefits so there's not the same degree of impact for most people and less have followed.
UHD is a step up from Blu-ray but you really need a large TV to fully benefit. I can see the videophiles upgrading their kit but there's definitely much less incentive.
I'm a big fan of HD in general but even I'll wait until the content delivery mechanisms have been fully sorted before I'd even think about getting a 4K TV.
If SkyTV starts broadcasting in 4K though then I'd definitely consider it.