"Parts upgrade" on crossovers -Any experiences?


I remeber upgrading the crossovers of a pair of B&W DM12's with esoteric resistors, caps and wiring (about 10 years ago). In the end I got a different speaker. The bottom end seemed improved and the highs were more delicate and smoother, but the midrange had lost some of the magic. I could not deal with the decreased midrange quality so I re-soldered most of the parts back to the crossovers but left the upgraded wire (the wire in there looked like tined copper and was tied with a Molex connector to the board!). I changed the parts since I felt that early 80's speakers could only benefit from higher quality parts and was worried that the cap values might be out of spec. I am currently using a pair of KEF 101 and I've been thinking about upgrading crossovers with Solen Caps, maybe some Caddok Resistors and Cardas or Kimber wire. The KEFs sound great but if I can get more out of them, I might give it a try. Anyone do similar upgrades with an increase in ALL aspects of your speakers performance...or have BAD results...or find the end result a mixed bag of better here, but worse there (like me)? Also, any input on what parts / brands to use and which not to use? Are Solen caps good choices (or are there others that work much better for this application)? Resisters Brands?
I am purposely leavig out the issue of active crossovers (don't want to find 4 identical monoblocks to run my speakers).
one_audiophile
Very interesting - as I posted in a recent thread, I had to have an under-spec'ed resistor that went bad "upgraded" on one of my Thiel 2.2's by the factory, whose tech stated that this particular resistor (at 1/4 watt) had caused many previous problems on this model. He just threw what he happened to have lying around (of the same ohm rating) in there instead - a 5 watt resistor of a clearly different type, and also gave me another one to install in my good speaker as a preemptive measure (he admitted that this wattage rating was actually overkill). I haven't done that yet, and this thread gives me pause. Maybe I should call back down to Thiel and see if I can speak to the head honcho himself by way of doing a little more research before breaking out the soldering iron. My one reassuring indicator so far - since I haven't yet re-broken in the fixed speaker, which also required two new drivers - is that the tech performed a quality-assurance anechoic test on the repaired speaker, and said it measured better (by which he presumably meant flatter, or within a tighter tolerance) than most examples of the model.
After reading these replies, I think that I will leave my crossovers alone. Sean and Rives have convincing arguments ( I've heard in the past about "breaking in" the caps and talk about the system aproach to crossover tuning ). I was just wondering if I was one of the few that had tried components upgrades with some NEGATIVE results. Thanks Albertporter for sharing your Snell experience (at least you got the Snells back to how they were). I will simply be happy with my current sound.
That's where I wouldn't mess up at all. There are a particular values placed and zillion times tested for a particular optimal crossover point.
All you might do is just ruin it to the different parameters and don't try to force yourself that your speakers sound much better after crossover mods(I know that many 'phools do) cause they simply won't.
You can experiment with electronic crossovers and bi-amplification doing much less harm and knowing that you're not wasting money for parts.
Post removed 
If you still want to try some upgrade here's two that don't involve changing crossover parts:

Put Bybee purifiers in line with the positive connection
to each driver.

Buy some sheets of Orca Black Hole Five(25" x 27"), cut
some piece to fit the inside walls of your speaker cabinets
peel & stick. Keep it free from the back of drivers and don't block the flow to any ports.