In my car, 99 Accord LX, I was in the same boat as you and considered putting tweeters in the dash (the grills were there but no speakers). I talked to many stereo people, and it was their opinion that tweeters in the dash may be too harsh, and a better location may be in the door or in the panel near the feet. I didn't feel like having the door panel cut, or a custom enclosure made, so I just went with a higher quality coax and didn't put separate tweeters in. For me, it was a good decision, but ultimately it will be your ear and you are the one you must please.