Crossover and Wiring Upgrade

Before going to the expense of swapping out expensive parts in a over. 

Consider which Wire Type can be used between Over and Driver. 

Wire Types I am an advocate of, are D. U. C. C

and PC Triple C. 

These can be a Sole used Wire or a mix for different Drivers. 

D. U. C. C will add a hint of a fullness to a base note, or enriched a Upper Frequency with a little weight to notes or vocal.

PC Triple C is removing smearing many many Wire Types add, it makes OCC sound muddled and veiled. 

If these Wire Types do what is suggested and are liked, why not extend their usage to being Speaker Cables connected to high quality copper connectors and also attached to high quality copper connectors on both Speaker and Amp. 

This will bring substantial and discernible improvement improvement.

The Xover can be left untouched while the new experience is being savoured.

If the Cover does come back under the radar, the prep' to get the best is already done 

OP,

What model SF speakers are you thinking about tinkering with?  
I know that SF use parts that some say are below what they should be using, but changing an iron core for an air core probably won’t make much of a noticeable difference. And on another vein,  mine have an 8 year warranty on them that I’d hate to muck with.  As others have mentioned, the resale value probably won’t go up a penny even though you added a thousand dollars worth of new parts.

OP,

If you are a believer of Cable and Amps, then your gear is resolving enough. With that said, and if your handy and good with soldering iron, then I think you should give the Speaker an upgrade. Just be sure you do not Frankenstein the Sonus faber

My piece of advice is to NOT change the component values, but change the crossover component parts brand, to say Mundorf, V-caps, Dueland and Jupiter. I get mine from partsconnection. It's easy to replace caps as you can read it, but for inductors, a bit harder specially if nothing is written on it. I have an Agilent LCR meter to measure inductance.

I have done this to my friends and my own home theater speakers (B&W and Klipsch) and I can tell you, i can here improve sonics and for the center speaker, a better dialog. So yes, just changing the brand of parts in the crossover can do wonders and its fun

again, YMMV

I'm tempted to say the change from iron core inductors to Jantzen air core inductors may have been the greatest upgrade to my crossovers. However, this after high quality film cap, point to point wiring, silver solder mods. In another speaker inductor replacement was less impactful. With crossover mods everything has to be taken on case by case basis, shouldn't apply generalizations.

Any crossover upgrade attempt has to be done with willingness to backtrack if your expensive substitution does not work.  There is no such thing as a universally better component—if something changes the sound, thst change can be for the better or worse.  The switch to air core inductors usually are an improvement.  Iron cores are usually used because they are compact and low cost.  
Different caps are tricky because people vary in their preference much more and caps take a long time to break in and stabilize; I’ve changed my mind sometimes weeks after an initial impression.  I observed a custom speaker being tuned to a customer’s preference.  The builder started with some very expensive paper in oil caps, but switched to “cheaper” film caps based on the buyer’s preference; the cheaper caps cost $400 each.