Don't know for sure what George had in mind but a wah is a guitar sound effects pedal. It's also the sound someone makes when giving a complaining cry. The song seems to have a double meaning here. One of how his inexpensive pedal was so effective in his playing it made him a big star. On the other hand he doesn't want the crying complaints of others to ruin his good mood, or sweet life. It could be a singing method too in which one puts a dramatic cry-like effect into a song. He may be saying that he doesn't need that to succeed in life or in his songs.