Full answers should be reserved for answers that actually answer the OP. If you want to add tangential remarks, they are best given as comments. If you have a remark that is too long to fit as a comment, you can add it as an answer with a disclaimer that it is only a comment on the answer by ______, but it's too long to fit in a comment box. Whether or not you make such "comments-as-answers" community wiki is up to you. In my experience here, if your comment is insightful and contains a disclaimer, you will probably receive votes up rather than down.

I think generalizations, history etc. are quite valuable. Although it doesn't get mentioned much, MO answers serve a dual purpose: first of all, the answer should answer the OP's question. But after the question has been answered, it remains on the website, where the software conspires to make it turn up easily on Google. That means that answers (and questions) should also be thought of as archives for future questioners (and answerers). From that perspective I think the value of interesting side comments is huge.

(What is discouraged, I think, is soapboxing.)