So I decided to roll an actual alt to level SMN with - instead of adding the job to Hiply - and I gave him a 200k gil boost to get going. At 55 he's in mostly 120s and has ~630k on him from doing almost nothing but MSQ and unlock quests. I expect that trend to continue, and unless I feel some need to buy glamour gear I'll always have more money than I need. Poetics are your friend.

One thing I will do, when I start getting rafts of V and VI materia from runs and/or hunts at later levels, is go play materia roulette where I will occasionally hit the jackpot with some decently rare crafter materia that boost my gil count. Other than that, off-job quest HQ quest reward items can sell really well too once you start seeing them.