Where does Aristotle say that it's better to know a little bit of higher things (e.g., metaphysics) than a lot of lower things (e.g., physics)?
It would seem this would be somewhere in his Ethics or Metaphysics.
In Aristotle's De Partibus Animalium lib. 1 cap. 5:
The scanty conceptions to which we can attain of celestial things give us, from their excellence, more pleasure than all our knowledge of the world in which we live; just as a half glimpse of persons that we love is more delightful than a leisurely view of other things, whatever their number and dimensions.
minimum quod potest haberi de cognitione rerum altissimarum, desiderabilius est quam certissima cognitio quae habetur de minimis rebus
the slenderest knowledge that may be obtained of the highest things is more desirable than the most certain knowledge obtained of lesser things
and in De veritate q. 10 a. 7 ad 3:
quamvis cognitio quam de rebus materialibus habemus, sit prior tempore illa notitia quam habemus de Deo, tamen haec est prior dignitate. Nec obstat quod materialia a nobis perfectius cognoscuntur quam Deus; quia minima cognitio quae de Deo haberi potest, superat omnem cognitionem quae de creatura habetur. Nobilitas enim scientiae ex nobilitate sciti dependet, ut patet in principio I De anima; unde et in XI De animalibus philosophus praeponit modicam scientiam quam habemus de rebus caelestibus omni scientiae quam de rebus inferioribus habemus.
Although the knowledge which we have of physical things is prior in time to that which we have of God, the latter is prior in dignity. And the fact that we know physical reality better than we know God offers no difficulty, because the least knowledge which can be had about God surpasses all knowledge about creatures. The nobility of knowledge depends on the nobility of the thing known, as is clear from The Soul. For this reason, the Philosopher puts the little knowledge which we have of heavenly things before all the knowledge which we have about things here below.