I just installed one of these a couple of weeks ago to replace the Roland 531 mixer I started with. I just dialed in my first big patch with it and so far I am very happy with it. The comments you made are right in line with everything I read on the ModWiggler thread, so I knew what to expect. My system isn't huge (2x 7Ux104) so I am not hitting serious limitations with stereo channels yet.
I am patching stereo voices into channels 1/2 and 3/4 for example and panning left/right. I imagine that I can also group voices using the mono channel A&B inputs as long as I want to control them similarly. Totally agree that stereo aux would have been great, and I haven't tried using one of the stereo channels as the return yet, but this is a suggested workaround. But I really wanted to just use reverb on the aux and control the amount of effect per voice, and it does that perfectly. OK it'd be better if I could use the stereo reverb but I am satisfied with mono on the effect. CVing the panning controls on the channels gives enough stereo imaging for my taste.
No power gremlins so far with the maxed out Intellijel case it's in. Mute buttons would also be convenient, but I am OK so far using the A/B switch for the channel inputs or just slamming the faders.
If anyone is thinking about this I highly recommend you read the full thread on ModWiggler. It's long but super informative and reveals a ton of use cases with potential issues, workarounds and alternative mixer modules to consider. What I was really impressed with is the active forum participation of WMD and their approach to problem solving. WMD steps right in to resolve issues very quickly and the customer feedback about WMD support is also great.
I'm really glad I pulled the trigger.