I nearly doubled the record: appx. 445,000 ducats.
As I thought, there was plenty of room for improvement with more innovation, though I didn't expect to have this large of an improvement. I will share my strategies this time around, because I don't think this can be beaten short of savescumming very hard for a better ruler. The strategy behind this run could not possibly have been better; every aspect lines up perfectly. You get a larger income return from developing gold mines than any other possible use of monarch power, so you only want to take the provinces needed and no more, because more is a waste of points that could be going into gold. However, you do also need land to give away for Revanchism. Mahafaly is perfect because Madagascar is isolated; you can conquer three of the nations on it and then leave the last one with one province, who is not threatened by anyone else and will not ally anyone else, making revanchism perfectly secured with almost no war exhaustion. The power base from Madagascar is enough to get you into Kilwa, and it's smooth sailing from there.
One of the priorities for this run was maximizing Goods Produced percentage modifier, which happened to synergize very well with what I was already doing: Golden Ages and Prosperity both reduce development cost as well, meaning more development on top of the better modifier. Fetishist is also the only religion in the game with the potential for a bonus to goods produced, from the Hindu cult, which I obtained by declaring a quick no CB war on Madurai. Beyond that, the rest of the run was spent at peace until time to give up my land for revanchism, to ensure that I would maintain prosperity for the end. This was another example of how perfectly everything worked out; because the land I was giving up was on an island, I had no chance of losing prosperity in my gold mines from the final war. Altogether, I had +45% goods produced. I was also able to get all of my gold mines down to 0% autonomy just in time through a combination of the Advanced Centralization edict and manually reducing autonomy by 25%.
As a note for anyone who hadn't realized, each 1 ducat of monthly income provides 4800 ducats at the end. Therefore, taking any amount of debt to expand rapidly with mercenaries, even over force limit, will greatly pay itself off at the end long as doing so generates a single extra ducat of monthly income. This was one of the principles behind my Ternate attempt, and I used it here as well to hire Lv. 2 advisors, and then Lv. 3, as well as build forts ASAP to reduce devastation and guarantee that I would have prosperity by 1485. My Ternate attempt ended with 5,000 ducats of debt as I continued to expand while over FL, but this attempt ended up being able to directly pay for its own expenses before taking loans due to the sheer profitability of gold mines.
I am incredibly satisfied with this attempt, and glad that I decided to try again, since I wasn't that happy with how my last one ended. I would be very impressed if someone came up with a strategy that could surpass this, short of finding a major new exploit.