Productivity will increase regardless of whether you are a programmer... My biggest problem is that I don't have any computer capable of driving it. That does change the value equation a bit.
I went to the Apple Store this weekend and read a document on the iMac 5K screen and then read the same document on the Thunderbolt display next to it and I found it a lot easier to read the text on the iMac. I have reading difficulties so anything that improves my ability to read faster is good for my productivity and also lessens fatigue from working long hours.
Like you, I'm in love with that 5K display. I'm so in love with it that I talked myself into buying that computer that will power it even though I hate what Apple's doing with the MacBook Pro line. I'm mosty going to use my MBP closed or as a second monitor with an external keyboard so it basically comes down to if I'm willing to pay a premium for stuff I don't plan on using just to get the monitor and the answer is yes.
I had to really think hard about going back to a desktop computer with an iMac to dodge the issue of having to take on a laptop I wasn't excited about, but in the end, having the option for mobility was too important and my need for a 5K screen is too big to put off the purchase for a more evolved MBP (if it even ever comes).
I'm a disgruntled Apple customer, but a likely to be very happy LG customer. How things change...