Aquila is optional, but the gear drops are excellent. The Blade of the Felled Titian from Kronus (side boss in 3rd Aquila area) is excellent, as is the Alpha and Omega Ring from the Gladiator (side boss in first Aquila area). In my opinion, only the ring and knife drops from Morganthe in her final fight are better.
Plus, much of the Level 30 gear dropped in the first area of Aquila is in my opinion the best gear in the game up until the WaterWorks gear (Level 60). I have a level 52 Fire who wears the Level 30 dropped gear from the first place in Aquila, unless she is fighting a Fire boss, in which case she wears the standard DS Grand Gear.
Aquila is worth doing for sure, even if you do it in stages as you reach each appropriate level for the next area of Aquila. The first area can be done at Level 30, but at level 30, the Gladiator may be a challenge. Pack Cleanse Charm TCs. Good luck.