If that's all he does, then what he really might be doing is prolonging the life of the crossover. I have no clue if they're susceptible to wear in a crossover like they are in an AVR or a PC motherboard, but when caps start to crap out, it's a problem. I know a guy who used to re-cap motherboards because he thought the caps made the voltage more stable.
He's also the only person I've ever seen do that, so take him being a crazy EE with too much free time with a grain of salt.
Electrolytic Caps will degrade over time. These should never be used in an XO. (Though they sometimes are.)
The Poly-Caps and NPE-Caps (Non-polarized elecrolytic) that are most common in Audio Crossovers are pretty stable as I understand it.
Usually, the main Inductor on the Woofer can easily be very large and will often be replaced by a Solid Core Inductor rather than the preferred Air Core Inductors, due to size and cost.
Same with the Caps on a Tweeter circuit: the main Cap will often be an NPE instead of Poly- or Film- Cap. The NPEs are smaller and much less expensive than their equivalent Poly Cap.
This is where things start to get interesting.
Many complain about saturation effect in an Iron Core Inductor. There are Steel Core inductors, too. Some say this Saturation is highly problematic in the Audio Band, while others say that the Saturation effect lies outside of the audio range. Either way, you start to see why some may want different components in that instance.
Similarly with Capacitors, you have higher ESR with NPEs that some insist is detrimental. Some of these then insist you can use an NPE but need to parallel a low-value poly-cap with it in order to eliminate that ESR associated with the NPE. Others still insist you must avoid NPEs at all cost.
*shrugs
The boutique designers I know DO NOT seem to worry about this in any way. They implement the components of their choice as they see fit, looking to balance cost and size of the XO circuitry while providing the high end sound they are known for.
It is important to keep in mind that switching out components for others can actually be detrimental to the finished product by, for example, changing the resistance inherent in an inductor.
Anyway... these same designers are not fans of using the silly "premium" components. They recognize that they are meaningless to the final product, even in a $10K pair of flagship Towers. They like to use Poly Caps and Air Core Inductors, when appropriate, but will also use some Steel Laminate Inductors and NPEs if the corresponding Air Cores and Poly-Caps are too large and expensive.
I asked one of these gentlemen one time if it was worth it to upgrade. He responded by asking if I was looking to gain something more. I told him that I didn't expect there to be a difference and was curious to his thoughts...
"I'll gladly charge you more if you want, but it's not going to change the Speaker. It's already designed the best it can be."
