Cheap ceramics leak and do not discharge consistently, which indeed alters their value and that problem is audible. All other caps of the same rating will sound the same in the circuit, however.
This is true, and in electronic circuits where significant currents are flowing it's an important factor, but we are talking about a low stress environment inside the passive tone circuit of a guitar. In this application the charge/discharge cycle time, leak threshold voltage and breakdown voltage are barely relevant.
The more important point here is that just because something is "vintage" doesn't mean it either sounds better or even different. Paper and oil capacitors, as used in many guitars of the 60s physically dry out and (literally) leak and change over time. There is a view held by vintage purists that if you want to duplicate a "vintage tone" you must physically duplicate the hardware that created that tone, so these people demand the bumblebee caps and other assorted BS. But Gibson used Sprague caps not because they were "better" but because they were available; just as Leo Fender used the 3/16 diameter Alnico slugs from auto magnetos for his single coil pickups. They may actually have been the best available in their time, but technology moves. No-one these days would choose a black and white TV over a colour one, or a Commodore or Acorn over a modern PC or Mac. Only the "audiophile" community seems to be hung up
old tech...
If we look at the Mylar film caps that are far more common in passive guitar tone controls than ceramics (ceramics and tantalum beads are often found in treble bleeds but not so often in passive low-pass filters) then I defy anyone to tell the difference between an orange drop costing £5 and and a "standard" mylar film cap costing £5 for a pack of 50. Objectively, the orange drop may be better; it may have heavier lead wires which break less easily; it may have, say, a 1% tolerance rather than a 5% and it may have a higher leak voltage and breakdown voltage, neither of which has much relevance in a simple tone circuit handling currents that are barely even measurable, but I genuinely believe that any perceived difference in tone is entirely in the mind of the user.
