There probably are dozens of us who have replaced x-over parts; I've done it to maybe a dozen speakers.
General advice is to replace lo-quality parts with hi-quality ones, but that advice is as useless as your question is general. Get to the x-overs, trace schematics, etc. Then we can help.
And we'd need a budget, too, as there's little sense to recommend you buy $300 of parts if you've have more like $100 in mind. BTW, $100 might be a good budget for the tweeter caps. My tweeter filters have about a grand worth of Teflon-film caps in them, but no one ever called me sensible. :-)
General advice is to replace lo-quality parts with hi-quality ones, but that advice is as useless as your question is general. Get to the x-overs, trace schematics, etc. Then we can help.
And we'd need a budget, too, as there's little sense to recommend you buy $300 of parts if you've have more like $100 in mind. BTW, $100 might be a good budget for the tweeter caps. My tweeter filters have about a grand worth of Teflon-film caps in them, but no one ever called me sensible. :-)