Parts cost/quality is so subjective, but my advice to you is this. If you have an itch to get your hands dirty build a new speaker from a kit. Then you can upgrade all you want to and be involved in every stage of the process. You'll learn a lot more this way and be more satisfied.
Upgrading parts in an existing speaker may or may not lead you where you want to go unless you've already done it several times. Rather than play with your perfectly nice existing set, I strongly suggest you get a hold of a good 2 way speaker kit from Meniscus or Madisound or even Parts Express and make it 100% yourself.