Is it worth contacting Sony to offer design tips?

Go for it, any effort to improve upon the lousy menu system of the NEX-5 models has to be welcomed.

Write to the head of marketing in Japan. Point out what's wrong with the current system, and how you would improve upon them. If you prick his interest he'll pass it on, and your letter/email will carry more weight coming from the top-down, rather than vice versa.

Good luck