Since your main interest is Ambient, a few ideas that come to me from quickly scanning your rig:
-- Joranalogue Morph 4 for blending / mixing signals in interesting ways. DivKid has a great video on that and his demonstration goes way way beyond what I would imagine the module could be used for.
-- maybe some of the "Chaos" modules from Nonlinear Circuits to add a bit of musical sloppiness to your patches?
-- some of the Rossum filters might be fun for you, like Linneaus and/or Morpheaus. The Rossum filters have really changed my idea of what a filter is -- e.g. it can be not only a filter in the classical sense, but also a more complex waveshaper or part of the soundsource depending on how you patch it.
-- for me, a lot of the joy of modular is in complex oscillators (like Make Noise DPO, Instruo C-sl, etc.) and waveshapers. These might not make a ton of sense in an Ambient setup? But when I see a larger modular setup (like yours) that doesn't already have a couple modules like that, I think "why not add some if you have room and $s"? For waveshapers, I particularly like Intellijel Bifold; Joranalogue Fold 6 and Instruo's shapers are also nice. All of those are probably a bit more controlled than the Plasma Drive (the PD I'm familiar with only through some videos).
My responses above are very much "free association," not at all a disciplined list of "must have" adds. And I know your post is UTILITIES focused; my list above is ideas across any module type. But I would hope at least 1 of these ideas above is interesting or useful for you.
Cheers!
Nicholas