I've been clasicaly trained on the violin, I've play it for years now, doing grade 8 next year, so I have a bit of insight in to this. I'd say yes and no. Yes because you know a lot more about scales and chord shapes and what not, so when you have a riff or a chord, you know what will go with it. However, sometimes if you know too much it is hard to write something original. My main instrument is guitar, and if i feel I'm getting nowhere I go and play with the piano, jumping in to that unknown realm always gives me unexpected and original results.