Check this out, some great DX7 style patches. Not sure if they are optimised for the DNK though, but the author studied the original patches and captured the spirit nicely.
As for the value, hard to say. Where I am located they are usually pretty rare. Lately there’s been an abundance of them, pushing them down to around €600-700. I don’t think that’s normal worldwide though.
I’ve been on and off getting one myself. I really love the form factor, it reminds me of the good old SFX-6 which I loved. But I do love the portability of the desktop unit too, and have convinced myself I can achieve what I want with an external keyboard. The Digitone is like two synths in one to me; one is an almost perfect and creative little groovebox with a world of sounds. Connect an external keyboard and it takes on a completely different life as a playable keyboard synth. I think you’ll love the DNK.
As for the DX7, I found it quite easy to get the hang of the interface. It’s tedious with a lot of button presses and jumping between menus, but fairly logical still.