Originally Posted by RonRizz

You can, very simply, replace just the door speakers. Leave the existing tweeters. Although running new speaker wires to the door speakers is advisable, it is by no means a necessity. Its been awhile since I changed mine out, but if I remember correctly, the tweeters are wired in parallel with the door speakers, and use only a capacitor to cut lower frequencies to them. Matt may be able to comment on whether or not I am correct when I say that.
Put in your new door speakers, listen to it with factory tweeters, If you decide it doesn't suit you, pop the grilles off, and unplug the tweeters. Problem solved.