Your house is 100yo (happy birthday!) That's a beautiful space -- and no hitting your head on collar ties. What's going on downstairs? Is the basement dry? modernized slab? dirt?? /windows/stone foundation?. All your living area windows new and tight? too much or too little ventilation in any combination between floors of varying tightness will all contribute to the froth in the attic. Think like a chimney. I wouldn't consider the MN climate humid, but you probably keep your windows closed 6-8 months of the year. Were you part of the recent heavy rains/did you have above average precip in the weeks prior to your noticing the condensate? If so, maybe this is the worse you can expect (this decade)
All the moisture in your house rises with the heat and gets up there in the attic. The warmest air, holding the most moisture, finds its way to the coldest spots and bam! Nealtw's right about once the dw is up that will help.
But you can still benefit from a thermal break. Perhaps before drywalling use insulation "tape" on the edges of the 2Xs. I seem to remember a company called Aerogel or some such. It doesn't have to be fancy. Its been years since I did it but I remember using an insulation from the blue or orange box that came in 6"(?) wide sheets and about 1/4" thick uncompressed. Rip it to size and install the drywall over it. Use SnoonyB's & MABloodhound's idea in tandem: caulk the cracks a bit, cover the boards (the boards themselves need a thermal break regardless of condensate) then drywall.
For the e-boxes: You can try the hardware store foam draft outlet covers. Of course that doesn't cover the receptacles themselves -- are they "airtight"? The boxes don't get messed with too often once roughed. Here's my seat of the pants: use some non-expanding spray foam in the deep of the box behind the receptacles. Maybe release the recepts, spray and quickly reinstall the recept. First find out if the foam is conductable or a fire hazard(!!). Need to work on the box? the foam is easily removable. Barring the foam, that same outlet cover stuff in a solid sheet could be cut to fit the back of the box and placed there. or use the left over sheet material from the 2x covering. go two layers deep -- it compresses.
personally I hate maintenance needing to be done every <period> passive or active. They're both time and energy sucks. Active is cleaning your gutters (where I am) twice a year. passive may be what you ultimately end up with in the attic: a dehumidifier. I appreciate the distilled water they produce.
I'll be quiet now.