A friend of mine took that much Valium (a low dose) for a few months, and said when he got off it he didn't feel fully normal for 9 months. Benzodiazepine withdrawal can be as bad as any drug withdrawals can get.
Benzos can have a lot of side effects even taken as per dr's orders. And they lose effectiveness by the time you develop a dependence on them. They're very useful medications for short-term or situational use, but as daily medications go, they're shit in my opinion. Most anxiety conditions can be treated with other drugs that have much milder discontinuation syndromes and aren't abusable. In my opinion (not that I'm a doctor or anything), benzos should only be taken daily if other options haven't worked and the condition is disabling (e.g., panic disorder).