to me, intellijel's cylonix shapeshifter wavetable oscillator & rossum's z-plane morpheus filter are two of the most awesome modules for sound design and mangling audio. to me, those two modules alone with a metasonix (etc.) tube VCA to grunge the digital tones up would be sicker than a full moog 55 system, but check the demos out for yourself and see if YOU like what they do.
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ring modulation is an "essential" form of distortion if you want to mangle audio every way possible. according to a review i read that praised the AJH synth ring SM ring modulator, they're not all created equal and that one, along with another name he dropped, were among the warmest sounding. it eats up a lot of space, but i'd say it's worth it if it's the highest quality, or at least in the "top 2" if the other one is even better.
bitcrushing is a unique effect. i'd toss a malgorithm in MY "tone bender" rig
if you're not planning on collection a bunch of specialty filters, intellijel's multi-mode polaris has a lot of analogue tone bending potential from juicy, to fat, to grungy.
to me... some tube grunge is essential. nothing sounds like a whizzed off all tube metasonix S-1000 wretch machine, but their tube VCA can really help thicken digital tones to add nice grunge. their slightly more expensive tube VCF variants might be even better, but i can't abide by an out of place retina burning yellow module mismatching my rack. LOL tube grunge seems underrated amongst modular fans, but as i've always been more of a sampler fan, tubes are essential for taming digititus and give synths the same kind of rocking tones they give guitars. there's a reason why tube preamps, compressors & EQs etc. are the darlings of recording studios.
i'm not sure i fully understand what it does, but from the description i read, pamela's new workout sounds like the mother of all LFO/clock modulators with its LFO "wavetables" (though as you've already seen... shapeshifter has gnarly LFO features too) and best of all programmability & memory. i dropped batumi & quad clock distributor from my play rack because it sounds like pamela covers everything they do & more, except maybe live knob & slider twiddling, but that's not my thing at all. i'd rather modulate in a DAW.
finally. i agree about rings. it adds a really distinctive sound to inputs.
as to effects, as i've always been more studiocentric in my research over the years maybe, other than maybe spring reverbs & distortion, i'd go with outboard effects as you can get A LOT of effects crammed in little multieffects boxes if you're not worried about tempo syncing (still possible with some units i think) and modulation, and there's a lot of really good VSTs too, though i wouldn't use them for analogue emulation, but convolution reverb & pitch shifting? why not?
if nothing else, i hope maybe shapeshifter & morpheus impress you as much as they did me.