I feel like I never ever really benefit from DoFs at all. Its usually a meal ticket for the AIs who manage to make a DoF with the human players. Because generally without fail, when you're finally enjoying great wealth and on very first turn of golden age, the AIs will roll around and start asking for DoFs and other ones that already have DoFs will want you to finance their bankroll for next 30 turns with golden age level of income which in turn makes your golden age feel like not a golden age at all. The worst this ever happened was that one time long time ago, I had five or seven AIs come up and ask for huge gpt from me for 30 turns on first few turns of golden age. I treated that as my handicap I give to the AIs who nabbed my gpt by rolling all over them with tanks after 30 turn period was over. They extort 1500 gold from me but they cant be bothered to spare a single luxury that they have multiple copies of for next 30 turns to the value of 240 gold. My citizens thirst for scrooge nations' blood. I was required to oblige happily.