There is some, but very slight, evidence from fossils that there was room for vocal chords in some dinosaurs, and others appear to have had resonating nasal chambers that would influence any sound they made. But think of frogs and geckos, then multiply their vocal abilities to dinosaur size and lung capacity! It's true we'll never ever know - and it's the same for all the imaginative colours and stripes and blotches they're given on TV. I think you've got it when you say it's just to add a bit more drama.