For me, "But my teacher never had to learn keigo in Japan. His wife is Japanese, and even she doesn't know much about it. " is a surprising thing to hear. In business (if you have a job in Japan,) if you cannot use keigo, I would say you will be fired immediately regardless of your nationality. I think teachers should have more responsibility to teach not only casual Japanese but also keigo. Also if you are able to use right (use it properly is important) keigo in your speaking, you will give more impression that you "have studied" Japanese properly to listeners. However, if you could use only keigo Japanese, it will sound a bit harsh. If your goal of learning Japanese is to communicate with only upto teenagers or friends, you might not have to learn keigo. So first, make sure of your goal of learning Japanese. I think what you need to do to acquire keigo is simply that you have to focus on studying it just like learning everything else. google what you are not sure, buy books, watch Japanese movies, and especially researching about business Japanese must be efficient. You can also always ask keigo questions to your Japanese friends or people on italki.

What you heard is a bit of exaggeration but I feel there is something in it. Most Japanese people don’t/can’t use full fledged keigo until they start working. as long as you stick with desu/masu speech style, you sound polite enough even with your teachers or someone upper. If you find it taxing, you don’t necessarily use keigo, but the thing is if you don’t understand keigo when they use it to you, your listening ability would be limited. keigo is mainly used in business situations and in the service industry, so people at shops, hotels and restaurants, talk to you with keigo. I have seen quite a few people who speak intermediate Japanese comfortably get stuck when they listen to people from these areas. My advice is getting used to listening to and reading keigo little by little, as you advance into upper level Japanese. That doesn’t mean you must speak keigo, unless you get a job in Japanese society. This might also help. http://www.maggiesensei.com/2009/08/27/%e3%81%91%ef%bc%9a%e6%95%ac%e8%aa%9e%e3%80%80ke-keigo/