Nearly mentioned chopsticks before but I doubt using them would do much, not for your clinch grip anyway.
OK, maybe the rythm you develop through playing some instrument can help you little bit to understand and get rythm in boxing. But also, you can develop same thing only through boxing.. If you boxed before playing guitar you should already have that rythm unless you are coached unproperly
You're probably right. But I seem to have trouble alternating between right and left roundhouse punches and need some extra training.
Serious note if you enjoy it do it, but don;t force yourself to do extra guitar sessions because what ever good you will gain from it you will have spent your time better doing shadow boxing or technique work.
It doesn't apply to all scenarios, you don't just improve from anything not categorically boxing-related. Building sandcastles. Not boxing. Irrelevant. Carpentry. Not boxing. Irrelevant. Yo-yoing. Not boxing. Irrelevant. See my point?