I believe, that with the high flammability rate of gasoline, that gas lines should be checked more often than every three years. Even if there was a system in place that meant a short check was done, and then a more intensive check was done every three years, would mean more safety measures were in place to ensure safety.
We have an aging infrustructure in the United States, including in existing gas lines. If we want to prevent leaks like the one in California we need to be checking these lines more often. It won't be cheap to do so but we put lives at risk if we don't keep a close eye on these things.
Gas leaks are a big problem once they happen, so I believe that if it is cost-effective to check the gas lines more frequently, we should do that. It can maybe even save lives, if a problem can be detected early and fixed if the gas lines are being checked maybe every two years instead of every three years.
No, we shouldn't check gas lines more frequently than every three years, because we don't have very many problems with gas lines. If there were more frequent accidents, we ought to put more time into checking them, but since gas lines are built very sturdy, there's no practical sense in checking them more.