My opinion, I don't think it is reasonable to spend twice the amount if that is actually what the difference is. First, there just isn't enough 4K material available yet, most of it is streaming. If you do some research the truth is as more people start trying to stream 4K ISP's will not be able to sustain the speeds needed. Here is one very good article.
http://blog.streamingmedia.com/2015/01/4k-streaming-bandwidth-problem.html
Second, if you wait and I don't mean for years, that price is going to plummet. Partly because that always happens but second because the economy is still horrible, nowhere near the amount of people needed to sell these to exists. Already there is a feeling most people will not see enough of a difference to jump into buying one if the cost is higher. (And that will be true for many people, many don't actually see 1080I HD now because of size of TV and/or distance sitting to it)
Get an HD TV that you feel is good now and I'm betting you could have that TV AND get a 4K for close to the price of what the 4K is now. And that 4K will be better than what is out there now. This is different than something better always comes along. It's just too new and price is not reflective of what it will be in the not too distant future.