Hmm... one other thought on advantages of Tractatus (which is also the plural, apparantly): You don't need to have a set level to read or write them, and your level does not affect XP gained. To write, you only need to have mastered the spell, which can be easy enough for low-magnitude spells (you need to know the spell to read). So writing Tractatus could be a sort of "poor man's" way of getting the covenant out of holes in our library and knowledge base, if we should have difficulty in obtaining other proper texts.
They're also likely to be at least somewhat valuable in trading to older covenants which are more likely to be composed of magi who don't get much use out of LQs and Summae anymore.
(And anyways, it's not a bad idea to master spells that would be cast frequently: multicasting and lack of botches can make for a nasty low-level spell.)