Is it good to upgrade the crossovers in your speakers?

I agree with sns, you can always go backward if a change is not in the right direction.  There are a lot of popular choices of current production parts that are not necessarily the way to go; vintage parts should not be overlooked even if the common wisdom is that they go bad with time.  Some of the best recent builds I’ve heard utilized such vintage caps as Western Electric paper-in-oil capacitors, Cornell Dublier caps, and Jupiter caps (not a secret, as many of these parts are ultra expensive).  Internal wire can also be quite important and the right choice can be hard to determine; a builder I know basically chooses between various types of Audio Note speaker wire, including crazy expensive Sogon wire.

johnk,

Yes, very good points raised.  This is like people raving about tweaks they employ.  Either they do, or they don't change the character of the sound, and if they do, why does it always seem to be for the better?  I suspect that bias is involved--people expect (or hope for) an improvement so that is what they hear.  

If one goes into these types of projects with an open mind, and the willingness to accept that a component swap may not work out for the better, then it is part of the hobby and I say go for it and GOOD LUCK. 

A local dealer who builds his own in-house speakers and electronics frequently encounters "improved" gear utilizing "better" parts that sound like crap.  Just because the parts are expensive and people rave about them does not mean that they will improve a specific piece of gear or will sound better based on the taste of the particular listener.  I heard one of his amps that had been modified by another company that was shockingly bad sounding (to my taste) even though the parts changes were of the same value (e.g., use of "better" Blackgate coupling capacitor).  In this particular dealer's speakers, Mundorf and Duelund capacitors are a complete bust, but, that is not to say that they won't work out in other designs; parts choices are very specific to the particular speaker an so one's chances of improving on the original design are not good unless one tries a lot of different alternatives.