If you're not doing any graphics work, I think programming can get away with pretty simple stuff. You don't need great colour quality, you don't need high refresh rates, all you need is to fit a lot of stuff on there...
Size does matter though. I like to have a browser, debugger, IDE with various windows, terminal, and some other stuff open. At work I've used a laptop with 2 medium-sized monitors, which works pretty well. But I prefer my two 2560 x 1440 27" monitors at home. I've found it helpful for the screen to be similar size, height and dpi, it feels more like one big screen.
Of course, since you're looking at it a lot, they can be used for a long time, and perhaps use it for other things like movies or games or stuff, you might well want to invest in good ones. But you can be totally functional without, imho.