I’ll chime in on the ModFilter:  The MF filters never felt deep / steep enough to me.  You can get some nice panning sheen with HP.  I feel its strong point is taking advantage of the ‘modulate the modulators’ aspect.  At times I’ve gotten better results with combining SHAPE – ENVELOPE and MOD SOURCE – ENVELOPE.  That’s a balancing act with DEPTH, SENSITIVITY, and MOD DEPTH.

That said, the envelope followers in the early algorithms are a strange breed.  Finicky to set up, easy to freak out, and kind of unpredictably sensitive to slight level changes.  Seems to me that they reach a ‘release’ threshold level, then drop like a rock.  Pass me a Slew Limiter, please.

Which brings up the compressor theory.  Either in front or behind, you’re changing the envelope of the envelope follower.  That might be useful … it’s been a while since I’ve experimented with a dedicated compressor inline.  Given the potential for peaky filter transients, I could see how you might tame those peaks with soft limiting.

Full disclosure:  I’ve been using envelopes over MIDI for the most part.  There are similar options for EXP PED input.  Highly configurable, and your target function can be any parameter.  It’s like graduating from an ‘auto-level’-type pedal compressor to a full blown dbx.  A little daunting at first, figure out the control functions, and then it’s second nature.