My own opinion is that vital music can be written in any style whether it be baroque, classical, romantic, modern, jazz, boogie, rock, pop, country, metal, even (GASP) rap.
For me it boils down to some sort of coherency that indicates the presence of a human MIND behind the music, and variety. Though sometimes I crave restriction in certain dimensions: thats what makes so many styles of modern popular music fun: How much variety can you create even though your harmonic, rhythmic, or textural language is very limited?
I used to be virulently opposed to really modern music like late scriabin or schoenburg. I still don't like schoenburg much but there's a great deal of modern music which is really well done and fascinating to listen to.
It takes getting used to---I listen to death metal. I didn't like the screaming/growling vocals initially, but now I crave them. (especially mike akerfeldt's death vocals from Opeth---very beautiful)
No matter what your harmonic language, it is possible to write vital music. (mainly because, I think, that the number of ways music can be mapped out through time [i.e. rhythm] is nearly infinite, even in the context of simple classical rhythm)
I do, however, wholeheatedly agree that such things as "chance" music, prepared pianos, anything by John Cage (well except perhaps one or two mildly interesting things), are the results of incredible, obnoxious pretense, and is an error of history that will eventually be forgotten. This isn't COMPOSITION, its nonsense, though it could be seen as creative sound-engineering/effects.
Oh and I'd like to add I think though its rare some people do like restricting themselves to old styles if only temporarily. Keith Jarrett's Paris concert starts out with some baroque styled improvisation. It probably breaks all kinds of baroque harmonic rules, but stylistically its very similar, and very beautiful. You wouldn't have known he was improvising it in fact!