Is it good to upgrade the crossovers in your speakers?

Ten years ago I had my vintage (1978) Large Advents and B&W 805 Matrixes (1997 or so) upgraded by John Van Leishout of Van L Speakerworks in Chicago. I pretty much gave him carte blanche within reason to upgrade everything. I know the caps, inductors, and internal wiring were replaced. The sound improvement was substantial in both sets of speakers. I recall that at some point he called me about various cap options for the B&W's ranging from $200 to $1500 per cap. I am pretty sure I told him to go with something in the $200-$300 range and that my "carte blanche" was not really blank. 

My recommendation is that if you are considering this truly for sound and not also for the fun of the exercise, than have a pro do the work. 

For those advising against diy or any crossover upgrades. Did you have negative experience with crossover upgrades? I've been doing diy crossover upgrades for many years, these have never changed the essential character of speaker. I've only experienced improved resolution, more natural timbre with the parts I've chosen. Duelund, Jupiter, Audyn caps, Path, Texas Components TX2575 resistors, Jantzen inductors, Duelund, Furutech internal wiring, never has a single one of these parts not been an improvement over original parts.

There is no magic in most original crossovers, parts often chosen because of cost or space constraints. Crossover upgrades can one of the most cost and/or overall effective upgrades one can make.

@sns et al

I have been considering the replacement of the capacitors in my speakers which are approaching 20 yrs old. I’ve always heard that 20 yrs is the life expectancy of caps, thus my concerns. Beside that is that I believe there is a slight loss of transparency over the years or expectation bias at work?, Even so, I like the overall sound signature I have and want to keep what I have, if for no other reason, the $12-15k replacement cost. I was told that if I replace with the same values, it should be fine

So, the question is it a good thing to do as a maintenance project? Then too, which capacitors? Nichicon made a big improvement to my 20+ yr old preamp. Are they appropriate for a speaker (original Silverline Sonata)?

Instead of buying overly-overpriced and overly-overrated audiophile caps, makes far more sense purchasing higher performance speaker.

Other than that, replacement premium quality caps can be found on generic electronic sites such as digikey.com or newark.com. They have Nichion made caps as well.

I replaced *everything* in my Thiel CS2.4s except the cabinets and drivers. Sounds much better than original. But it was a lot of work and expense. And fraught with the possibility that I would screw it up. Important to match values of original parts (well, ok to increase voltage of caps or wattage of resistors) and make sure that total series resistance is close as possible to original circuit.

As for capacitor life, electrolytics start to degrade after, maybe, 10 years and should probably be replaced by, say, the 20 year mark. But film caps are very stable, essentially lifetime caps.