To answer is it worth it, is difficult for me to do for someone else, as people disposable incomes vary and what not.
But Ill try and answer some of your question and give some of my thoughts. Firstly your second question first. FM synthesis is probably more famous for being an upfront, more abrasive sound rather than what you typically might associate with chillout or ambient, but the beauty of its implementation in the digitone, and through your on programing with the use of filtering and FX, in my opinion the digitone has no issues creating those type of pad sounds. In fact using the sequencer and plocks in subtle ways can help produce nice evolving pads sounds, not to mention using the LFOs + envelops per track.
Was it worth it for me?.. probably not so far, because I’ve not used it as much as I should have, But this is on me, rather than on the synth, I just have found lately I’ve reached out to my more knob per function synths. When I have used it Ive loved it.
Would I sell it? no way, for me and the money I would make back would not really be enough to fund much of anything else I have my eye on, plus there are pieces in my studio that I use far less, and I’m not really inclined to go use again, these would go first. I am definitely intending on using it again in my next track (a decision made whilst writing this response).
Not sure if any of that is helpful, just my experience so far, but like I said my experience is not over yet, its still going