If you want to learn how to read notes and stuff but still have percussion, xylophone (and mallet percussion in general) would be the instrument to learn. It has helped me a lot.
That's what my drum teacher is like, he can play keys and even composes his own percussion pieces, but he wouldn't be doing it without learning both marimba and drum set.
He states that it improved his drumming, makes his technique precise (eg. hitting small keys with mallets) and that his drumming becomes more musical.