I don't watch a lot of TV but do watch a lot of TV programmes that I have downloaded on my tablet. My 40" 1080i screen from 5 years back seems perfectly adequate for TV broadcasts (most of which seem to be in 720p anyway) and also for Blu-Ray. The TV in our room is now for communal/social watching of films, sports events etc. It has become a special occasion device for me rather than an everyday device.
As with other people on here I doubt I will replace my TV any time soon. I haven't seen 4k in action and may consider upgrading in a couple of year's time but the difference would have to be substantial. I would rather spend the money on a nice speaker set-up instead (TV speakers seem to be absolute garbage).
I have noticed that hardware seems to have outstripped software substantially. My PC is around 3 years old (an overclocked i7) and the only things I have changed is adding an SSD and a new graphics card (along with new power supply to support it). I can now play any modern game and the load times for Windows 7 and programs are astonishingly quick. I cannot see me upgrading the PC (e.g. new board/chip etc) for at least another 3 years.
Likewise my HTC One that I bought over a year ago I wont change for another year at least as every app and Android itself runs perfectly.
I once thought the hardware refresh cycle would mean significant spend continuously to keep my gadgets bang up to date but I'm sure my wallet is grateful for not having to do that!