IME, having a smooth directivity between drivers is important in highly reflective environments like a car. It's not as important when you are listening to let's say nearfield studio monitors in a larger space where the room reflections are not contributing nearly as much to what you are hearing.
But listen to those same studio monitors that have poor directivity matching in a reflective room and in a more mid-field or far-field scenario, and they lose most of their magic.
In a vehicle, we can't really get away from all of the reflected energy. The reflections are a major contributor to the sound in a vehicle, so IMO, having smooth directivity between drivers is more desirable. It affects both tonality and the imaging cues.
IMO, choosing the best tweeter that you can along with a true high-quality midrange, and using both in an appropriate passband to minimize the delta in directivity is the way to go, and it will provide the desired "air" and ambience.
Though I can't say I've done much experimentation with good "widebanders", as the erratic high end response above 5k-6k in most of them keeps me from going that route, along with the potential beaming issues.
I'm sure you've read
@Ge0's "comparison" thread, and I tend to agree with the majority of his impressions. The Focal TBM, Morel Piccolo v2, and Audison Thesis Violino v2 really give you that special 3D "air" and holographic space...and the BliesMa beryllium as well.
I first heard the newer Focal TBM beryllium tweeter variation in the Trio11 Be studio monitors, and let me tell you, they are somethin' special. It blew me away.
Using differential rear fill can also help in this regard, but it doesn't work consistently with all music.