It never hurts to LOOK for a higher paying job. I try to interview at 3 different places per year, even when I'm not actually wanting a new job. It does a couple things for me:

1. Keeps me and my resume fresh on interviewing. I don't want to be in a situation where I lose my job, and haven't interviewed or updated my resume in 15 years.
2. Gives me an insight into what the market is looking to get from someone in my position. What can I change about what I do to be more effective/desirable?
3. If I receive an offer, it lets me know what the market rate is for what I do. I can then use that information to request a raise at review season, if it's reasonable.
4. It leaves me open to amazing opportunities that come my way. I got a a 28% pay raise to do an almost identical job, because I was open to the opportunity.