Reading through the OP again, the sound design, interesting melody lines timbres and sequencing possibilities…
I agree with your gut to not do another elektron box. You want something to take you in a different direction. The question is more fundamental:
Do you want to “play,” do you want to “sequence,” do you want to “write” or do you want to be “inspired by sound” (sorry couldn’t squeeze that last one into one nifty word).
If you want to sit on your couch and play out melodies, the op-1 is a good fit for this style and the tape metaphor will push you to think differently than you do with our Elektron devices. What you lose (imo) is the ability to take it back to your studio / desk rig and incorporate it flawlessly. It has always felt very contained to me. And that can be good, it pushes different creative buttons, but it can be limiting. On the other hand, you can sample to tape from your modular and then take that to the couch and layer and overdub and work on ideas, so there’s some benefit there. It also has a fun factor (all of this is the og, which is suddenly highly available on reverb for some reason)
If you want to sequence, I can’t recommend the deluge enough, and I’m still struggling to understand why anyone would pick the polyend play over it outside of the screen. It can sample, loop, multisample, do va synthesis, simple fm, wavetable synth, euclidian sequencing, you can set a different sequence length per note on melodic sequences or drum sequences, has a robust song mode, and solid midi implementation with mpe for when you get back to your desk. It has a battery and streams samples straight from the sd card, so you’re limited only by the cpu eventually choking. The limitations are it takes more time to learn its shortcuts and workflow without the screen and the engines are “okay” but not particularly inspiring - but for building ideas outside your normal workflow, it’s sequencer is really underloved in these parts.
If you want to write - the m8 is the absolute winner. It’s the closest to the elektron workflow as they’re really just tracker brains in 808 bodies. This one also gets the honorable mention for “inspired by sound” as it has such a wide range of synth engines with the full braids set, a wonderful sounding 4 op fm engine, sampler and all of which share a common 2 envelope 2 lfo multimode filter, drive, reverb and delay structure after the osc. This is a great place to get a basic sequence going and then just start messing with your patch until you’re in love. Downsides are it’s just not as immediate for “playing” or sequencing as the other two, but having all of these in my life, it’s the one that is never not in my laptop bag and always comes out. It’s also an audio interface and so you can use it with a phone or ipad with a connection kit to expand its universe.
The other key for me is on the couch, the less gear the better. I don’t want a powerbank or a secondary keyboard or device. I really want something I can just chill with, and so that’s either going to be the m8 or my phone or tablet (the arguments for the ipad are strong here, and not needed to be repeated, but I think these three devices all have specific merit for getting out of your normal zone).
So, all told, about €750.