Answer

First, it is permitted to engage also in optional matters. That is how all the halakhic authorities inferred from the contradiction between the Talmudic passages in Berakhot and Menachot. Second, with respect to Maimonides there is certainly no difficulty, since in his view science and philosophy (the Account of Creation and the Account of the Chariot) are a great matter, whereas the discussions of Abaye and Rava are a minor matter. Third, even without going as far as Maimonides did, it is clear that these are worthwhile fields, and it is important to study them even without there being a commandment to do so (see the responsa of Rabbi Moses Isserles, section 9). In my view, this kind of engagement is Torah on the level of the person (even if not on the level of the object studied). You can search here on the site for a fuller explanation.