You are more fortunate than you can possibly understand right now, because you’re asking yourself these critical questions at the perfect time. Almost no one worries about these things until it’s too late; but because you are worrying about them now, you will have a richer life.

I got my B.A. in 1980. Life is full of regrets for everyone, but some of the things I regret the most are skills and knowledge that I allowed to decay and disappear. I used to be able to carry out rudimentary conversations in French, but, from disuse, no more.

Yes, it is absolutely worth knowing chemistry just for the sake of knowing it (and I say this as a physicist who never liked chemistry). As you know, it takes sustained, active effort to really learn anything about a subject, but, without some kind of knowledge maintenance, that knowledge will disappear over time without you even realizing it. Keep your textbooks (do colleges still use textbooks?). Make an outline of the subject and the parts that you don't want to forget. Make flashcards (I use Anki) with facts that you want to keep in active memory. Periodically, for the rest of your life, consult your outline and refresh your understanding of the subject, through your textbooks or any online resources that seem useful. Have conversations with people interested in chemistry or anything else that you want to keep alive in your brain.

The advantages surpass “for the sake of knowing it”. All of human knowledge is connected in a vast web whose nature we can barely see. If you maintain your knowledge of everything you have learned, you’ll eventually able to see some connections that neither you nor anyone else can imagine now. This, increasingly, is where new knowledge is created: at the boundaries between what we believe are separate disciplines.

More fundamentally, it feels good to know things, and to see the connections among things. Do it for this pleasure.