Capacitor

As someone else mentioned the values of every component in the crossover are the more important in the voicing of the speaker, taking into account the character and limitations of the drivers used together, than the quality of the crossover components (well almost always).

Could a better engineered crossover for a particular group of drivers, taking into account their measurements, particularly breakout, frequency response, impedance curves, anti-phase measurements with lower grade components beat out a higher quality crossover in parts? Absolutely.

However, recreating the same circuit (within reasonable tolerances) with better engineered components that will introduce less noise, not choke transients, and reveal more detail is almost certainly going to produce a better sound.

How much to invest, and where the diminishing returns lay, is how well the drivers could possibly play together, how the cabinet works, and the crossover points implementation on the chosen drivers...

Duelund JDM Silver .01uF bypass cap - yeah, you might want to research this, it’s a gem of an upgrade for little outlay.

Even Troels with all Z caps = xovers cost more than the drivers,,!!!!!...
Can not match a high sens performance in mids/highs.- mozartfan

How much to invest, and where the diminishing returns lay, is how well the drivers could possibly play together, how the cabinet works, and the crossover points implementation on the chosen drivers... - rixthetrick

@mozartfan - There's no surprise superior engineered drivers will produce a better result.

Yes, it is more complicated to know where and when to spend the money to get the best results for the investment. I am assuming you didn't just upgrade the capacitors and nothing else in the crossover networks? 

There's no blanket statement for crossover upgrades in the many varying speaker designs out there, on that we wholly agree.
Though, depending on the parts used, upgraded parts can be as results varying as using different ingredients in a recipe - substantial differences.

@paulcreed - thanks, I'd never looked at Miflex components before, thanks for bringing it to my attention.