I replaced my tweaters this weekend with some polks. If you go out to element-j's website ( http://www.ecnet.net/users/gallery/element-j/ )
he has pictures and directions for getting to the tweaters. You should probably have a custom mount to replace the factory setup, but since I was lazy I just used duct tape to hold the tweater in place. Ended up cutting the oem wire between the tweater and the wire harness, and then soldered my new tweets to the remaining wire coming from the wire harness. Sorry I didn't take any pics, but it is doable and it sounds great!
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
By the way... the overall affect of all the new gear versus stock is quite impressive. 8)
You know, I love the stereo in the EX... it was a major selling point for the car... but the tweeters do seem a little on the harsh side, even when they're only on +2. Doubt I'll replace them though...