This is most likely a simple issue of miscommunication, don't get so worked up over it. Given your level of experience and good track record, your boss and the higher-ups are probably making plans to move you into a different role, where they see you would be valuable.
Of course, they have to bring in someone new to take over the work you are currently doing. The boss should have ideally communicated this to you already, but humans make mistakes. Maybe he simply forgot to tell you, or he thinks you have other work to do and doesn't realize that you are idle, or he doesn't think this is critical enough to tell you now and plans to tell you later, etc.
I would strongly advise against bypassing the boss and complaining to the higher authority. If it turns out to be something like the above, your boss will wonder, "Why didn't you just ask me first, if you were so worried about it?" and both you and your boss will lose face.
Tell your manager that you have been idle for a while, and ask him what are his plans for you. No matter how much this frustrates you, don't drag the newcomer into your discussion or blame the boss, that is, don't say something like, "Hey Boss, why did you bring this new guy, and give all my work to him?" Focus only on your work, complaining about others (or even appearing to be complaining about others) doesn't help you in any way.