Rhythm matters a great deal in writing. You just have to have it. If you can't find the rhythm in your work, then you're probably in trouble.
Now different languages favor different rhythms in speech and writing -- I speak barely enough German to know that -- and there're pronounced differences in the natural styles of writers.
Does this mean some writers have styles that naturally fit certain languages? Maybe there are people out there who can't write in English to save their lives, but who would have been fine in Swahili, if only they knew the language?
Or are there writers who can be improved by translation? I'm thinking of Perez-Reverte on that one. I don't know a word of Spanish, so I can't speak for the original, but the translations of books like The Flanders Panel are brilliant. (If you haven't heard of him, rush out now and get The Flanders Panel, The Dumas Club, and The Dancing Master).