Your subject line and post are asking two different questions.
Is there a "point"? That depends on you. Would you feel comfortable being with a partner your whole life and never being able to understand when they speak their native language? Of being left in the dark or having to depend on that partner every time you go to Japan, or interact with their non-English speaking relatives? Would you feel comfortable knowing that your partner can communicate fluently in your language (or one of your languages), while you are essentially completely helpless in theirs? If the answer is "yes, I'd be fine with that," then I guess there's no "point."
For me, I couldn't bear the thought of going to Japan and not being able to function as an educated adult, so I never once questioned if there was a "point." (This was before I had a Japanese partner.)
If living in Japan I think IMHO you must learn it anyway as you don't want to rely on your partner for everything. In my first years in Japan I had to rely too much on my wife because I didn't make enough effort to learn the language before I came here and I hated it... She got pretty tired of it as well.
Besides that I think learning your partners language, no matter where you live, is showing respect to her. This doesn't only mean the language but also culture.
Like mdchachi, I avoided girls who spoke English and job that does not require any Japanese, learning and mastering Japanese was a motivation for many years,
I enjoy impressing Japanese people and foreigners alike with my Japanese skills.
A job that require to speak Japanese 100% of the times is the best way to make progress, and it helped me tremendously to go over the 2kyuu level, but it is not always the best jobs as it just put you at the same level as the Japanese or lower, if you are not Asian it is harder to land that kind of job especially for customer facing roles.
Good Japanese skill can give you a edge at job interview to land a good paying job at a foreign company, once you get that job however you won't have much occasion to practice your Japanese because people at those high up companies don't expect foreigners to speak or understand Japanese.
Knowing Japanese is still useful in Japan to land a job, read bills, contracts, health reports, quotations, etc .. I often found that my wife don't understand things very well and knowing Japanese help save some money on multiple occasions. Only drawback is that you only have to prove you can speak Japanese, you have to show off a bit when you go somewhere so that people understand that you are not a tourist and can understand Japanese, also it can be frustrating when you have someone who somehow insist on speaking English to you, so you can end up in a situation where you the foreigner speaks Japanese and the Japanese speak English, if none wants to give up and a lot of weird situations.