My general advice to you is
If It Ain’t Broke, Don’t Fix It. Leave the individual drivers, the internal wiring, and the crossovers as they were built. If something is wrong, it should be identified as much as possible, and repaired. Otherwise, listen to your speakers. Don’t judge their sound by looking at them – especially inside.
If you hear “something wrong” only on certain pieces of music and at a certain volume level, it probably isn’t a bad voice coil. Can you describe this noise better? High or low frequency? High or low volume? Something may really have broken or failed, or this is inherent to the original design. So far, I can't say which it might be.
The existence of “cheap zip cord type wiring” inside an expensive speaker should reveal something important to you. Although many speaker manufacturers pay lip service to customer use of expensive or boutique speaker cables
outside the cabinet, they ignore that
inside the cabinet. Ignore your audiophile instincts here. Copper zip cord of reasonable thickness (18 gauge is alright for short lengths) is all that is required. Shielded wires are unnecessary. Resist the urge to “upgrade” the internal wiring. If It Ain’t Broke, Don’t Fix It.
Those connections between the wires and individual drivers may also look shoddy to you, but if they have survived 20 years, how bad can they be? Again… If It Ain’t Broke, Don’t Fix It.
The article linked at the top of this thread did talk about the advantages of drivers with cast instead of stamped metal baskets. However, it was meant as a shopping guide for people buying new speakers. While it is true that cast metal baskets are a sign of better quality drivers, it isn’t true that drivers with stamped metal baskets can’t also sound good. The same is true for the magnet size.
In your case, you already own speakers that I think you like. Mirage selected the original drivers and designed the cabinet and the crossover for them. If you replace the original drivers, you might as well get all new speakers because the cabinets and crossovers will have to change as well. You may not approve how your speakers look on the inside, but you do seem to like how they sound.
Yet again… If It Ain’t Broke, Don’t Fix It. I hope by now, you are seeing a pattern here.
Linkwitz-Riley is a type of crossover filter design that can provide better frequency response across the crossover frequencies than other designs. It isn’t a crossover manufacturer. In your speakers, Mirage probably designed and built the second order L-R crossovers.
Now you are making good sense
. Give Mirage some credit for designing what seems to be a good speaker. Many other people besides you have imagined they can “upgrade” their speakers by rewiring them or buying different drivers or crossovers and simply dropping them in place. While speaker design isn’t quite rocket science, it isn’t as simple as child’s play either.