jdef: It's gonna be really hard for me to give you a good response on this one. :? I replaced the radio, all four door speakers, and the tweets all at the same time. So, I have no way to give you any incremental feedback as to the value-addedness of just the tweets. If I were making a general recommendation for sound improvement it would be in the following order:
Front door speakers
Rear door speakers
Head Unit
Tweeters
By the way... the overall affect of all the new gear versus stock is quite impressive. 8)