I agree with moxxey. I have been buying Apple's Macs ever since 1985. Whenever I bought one (and there have been quite a few) there was something better that came along shortly afterwards. After a while you realize that this is quite OK, and that you do not have to trade "up" whenever a new spec is available. In the case of the Macs I'm probably not using more than 15% of the processing power in the one I'm using now, if that.
As to image technology and resolution. It will keep improving. I hung on to my BeoVision CRT for a long time, until I finally saw flat panels catching up over the last twelve months. I now have a plasma screen and a BeoVision 8, and I know I'll have them around for a long time, providing a lot of viewing pleasure -- no matter what's coming down the pipeline!
We already have flatscreens with a resolution they can't really display (Full-HD) intended for large screen projection. And people are speaking of higher resolutions yet, in the tech-spec wars taking place between manufacturers. There's a point at which one should say: this serves my purpose.
I will grant you that having a fast pulse (100Hz) screen is probably preferable to lower rates. Though you should realize that when you're in the cinema, you're watching 48 Hz projection (each image is shown twice, to trick the brain past the threshold where it discerns between separate images) -- and cinema projection works alright, doesn't it?