Cant say on the temperature related fluctuations, thats something I've not looked into that for tone shaping caps on either guitars or amps. I HAVE looked into what happens to electrolytic caps with temperature, after having them blow on a few ABIT motherboards (on the main processor power rails) and in the amps I've made. Conclusion there is to overkill, since filters tend to run hot, and tubes are hot and well... heat is no good there.
But, for a guitar, or in the tone stack or coupling of amps... heat is not really a huge deal....
The ESR is a big deal, but again, really in amps more than guitars. In amps, Orange Drops, to me, have that "JBL" tone. Clarity, sparkly, tight. Some say too bright, maybe even brittle. The Mallory's are darker.
As in resistive elements effecting the tone response, caps also have a resistive factor in their list of properties - the effective series resistance, or ESR. With a resistor you can add "series resistance" to a circuit, not shunted to ground, and it will darken the tone by attenuating the high frequencies. This is due to resistors having an impedance property as well as a pure resistive property. Thats a trick to use in amp tweaking.
Back to caps... In a tone control on a guitar though, we're not putting the signal through the capacitor, but shunting some of the signal to ground with it. Normally we might say a value of X will have such and such db loss (say 6db) at frequency Y, when the inductive reactance of the pickup is Z (not factoring the additional capacitance of the guitar cord, or the loading of the controls, or loading of the input of the amp - generally pretty high impedance anyway). In a guitar, the current flow is so minuscule that changes in things like ESR of a capacitor really don't have a huge effect on the attenuation of highs when the capacitor is used as a shunt to ground. That is, the resistive property of the capacitor is not "holding back" some of the highs that normally would pass through to ground, because the current flow is beyond tiny and the IR drop in voltage doesn't amount to beans. Hard to think of an IR drop through a capacitor but it is one thing that can be considered when the voltage level and current level are greater... as in amps.
In more plain English - the type of your capacitor generally doesn't do squat, unless you look at the extremes of secondary properties. In amplifiers - tube amps - the type of capacitor seems to have a greater effect. Not withstanding - there is also a thermal noise factor... that must also be accounted for, just like certain resistor types are thermally noisy. Again, amp stuff, not guitar stuff.
Hope that helps.
