A bit of new news on this: I have another Performa 520 that's been sitting for several years that I got at VCFMW 2023 without drives or logic board as part of a deal I made with a seller in the parking lot. I figured I'd take it apart, look things over, and decide whether to recap the analog board and have it as a "parts" thing, or perhaps just sell it and the CRT. After I pulled the CRT, I wanted to look at its microphone. To my surprise, there was absolutely zero leakage or corrosion from its capacitors, and the labels on top were different from my previous Performa other than the 4.7.
Since there was no leakage, I easily pulled the caps and measured them in my meter: If they're 4.7uf these are quite out of spec and the ESR/Vloss are terrible. They're definitely on their way out! But given the age and the lousy components used back then, this kind of drift is inevitable. I'm still still not sure of the voltage but given the old parts' small size (higher V parts = larger physical size) and my uneducated assumption there's not much more than 12v going through any part of that circuit, I'll say anything 25v or higher is safe here and they're definitely 4.7uf.
Side note: I wish VCFMW would do a "rebrand" like macOS/iOS/etcOS did recently and forward-date their events by 5 so this year's event would be officially called "VCFMW 26." Or maybe they can host two a year until they catch up? Ah well.
