OK, so I spent a whole week with just the DN1 on the table, nothing else… 
It’s been fun, I’ve learned a lot more FM tricks, and made a whole lot of sounds that I wouldn’t have attempted with FM. FM is definitely something you’re better off studying then just sitting twisting the knobs. Fortunately there’s hundreds of videos out there to teach you the tricks of the FM masters.
I found the DN1 keeps you much more focused than the DN2. The big Problem I have with DN2 is that I’m constantly wondering if I’m doing it the right way, or if I should be using a different machine. More choice isn’t always good.
I have to mention the factory presets, too. The DN1 presets are brilliant, there’s a ton of usable sounds there and loading/tweaking them is a good way to learn. DN2 presets are horrible by comparison.
Finally: The DN1 has helped me understand why the DN2 is the way it is. There’s a few types of sound that a DN1 simply cannot make, the DN2 fills those gaps with WAVETONE and SWARMER machines (and to a lesser extent with FM_DRUM).
Gaps in the sounds engine aside, the main problem with it is the lack or tracks. Four tracks is really tight, especially for drums. You can try to put all the drums on one track but that has a lot of limitations and makes it really hard to tweak sounds in the melee of trigs (eg. change just the snare sound). You also can’t mute individual sounds.
Apart from that, it’s a blast. Everything just fits together perfectly, they really got it right on this one.
The button layout should definitely have been carried over to the DN2, particularly the row of buttons under the encoders (which is totally messed up on the DN2, IMHO). A DN2 with 8 DN1-style track buttons on the right hand side and 16 voices would have been the way to go.
Am I going to keep it? I’m trying to come up with an excuse but I know I probably won’t. A desk can only hold so many Elektron boxes and my DN2 is far more capable, even if the UI is a step backwards.
Edit: Or maybe I could sell the DN2 and use the DN1 to play my Syntakt polyphonically through my RK002 MIDI cable. I really need to try that… 
So… to answer the question: “Is it worth it?”
The answer is: “it depends on what else you own”.
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If it’s the only instrument you own: It’s a nice toy but has some serious limitations (eg. number of tracks). You can do a lot but you’ll want to add something else eventually and put those MIDI tracks to use. A little subtractive synth… or maybe a DT1 might be a fun pairing - you could make drum sounds on the DN1 and record them directly into the DT1. This leaves you with 4 synth tracks on the DN1 while the DT1 does the drums.
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As a sequencer and polysynth in the middle of a studio setup a DN1 is totally worth $375.
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If you already own another Elektron box then the sequencer is less valuable but even as just an add-on polysynth (eg. to a Syntakt or Digitakt) It’s worth that much.
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As a learning experience? I’d recommend a DN1 to anybody who’s thinking of getting a DN2 in the future. You’ll get far more out of a DN2 if you’ve spent a few weeks with a DN1 first. Prices aren’t going down, you can resell it for about the same as you paid for it.