Schneider's Buro shows the Happy Nerding Isolator on their site, but lists it as 'coming soon' in its status bar. My guess is that we'll see it available right after Musik Messe, which should be in mid-April. IMHO, something like that might be worth the wait, plus if it's in your second buy, it should be on the street by then.
Buffered mults...well, when you need them depends on what you're splitting up the voltage TO. Some modules drop the voltage worse than others, depending on the impedance loading at the CV input. But since we're dealing with three Intellijel VCOs and a MakeNoise Mysteron, I'm not inclined to think that either David Dixon or Tony Rolando would design something with crap loading on the inputs. Generally, the rule of thumb should be that once you pass six splits, then you need to regenerate voltages, but some VCOs...not these, though, I'm sure...can be problematic in a split between just 3-4. If you're still concerned, just drop one of the buffered mults; this leaves plenty of regenerated signal off of just the one remaining. Mind you, the critical need for buffered mults only really comes into play when you MUST have the same exact voltage scaling between the splits; if you're splitting gates, triggers, or non-critical signals like LFOs or other modulation CVs, they're not all that necessary.
ooooo...comb filter! Have I got a filter idea for you: a Doepfer A-106-1. Sallen-Key pair, like in the Korg MS-20, but with a sick little twist: an insert point in the resonance circuit! Now that little detail opens up a lot of weird stuff, especially when you drop a short delay into it like...well, a 2hp Comb. What would be happening in such a configuration is that the regeneration for resonance is being delayed by a teensy bit, causing the whole filter setup to 'whunnnngggggg' very strangely, creating (in theory) another resonance structure in the path. I like this filter...I've loved the nasty, alternately fat and yowling character of the MS-20 for decades (and Dieter claims his version is even grittier and nastier than the original!), and having something utterly insane like that insert is a bunch of plusses. Another bit of filtering bad craziness is the Mannequins THREE SISTERS...formant-structured, but with this odd 'centre' input that causes the formant spacing control ('span') to go into warped FM-type behavior in the filter circuit. Consider: mult your input signal to that, and split one feed off to the Comb, then send it from that into the 'centre' input. Wooooooooo.... Happy Nerding, also, has an unwell filter, the MMM VCF, that allows you to either use it as two ganged state-variables (that also happen to have a 4-pole LP out, atypically)...which you can also feed into each other in various configurations to create some very weird filter behavior, plus the Comb can be linked into that sort of a signal tangle to make things even more unreal. Basically, anything that lets you subvert the normal filter behavior in some weird way or another, like those three examples, might be the sort of thing you're looking for. Loads of abuse potential...just like adding those 2 hp mixers; a little alteration in the way of thinking about the signal flow can yield amazing results, very unlike the things you find in a typical analog modeller.