I've come up with a small list of things we can spend a Great Deed on to get us more money.
-A new fief. Not only will this get us more money, it'll also bless a number of Imperial subjects with our fair and august stewardship. I'm taking the piss but they would in fact be better off under us than most other nobles.
-Hiring the Imperial Engineers School to build and maintain a bridge, lock, road, series of signal towers, or other civil engineering project for the benefit of the EIC. In
this update, we see that there's mercantile value in getting information quick. In the case of bridges, roads, and locks, we could charge tolls for non-EIC to use them.
-A trade ship built to our specifications and put under our permanent command. On top of making us money, it also gives us transportation to other parts of the world without being limited by the fuel, size, and weight limits of our gyrocarriage, and depending on the specifications, it could increase the range of the gyrocarriage. The ship could also be used to go and purchase items of interest in other nations we can't get through our current means, like Esoteric Bretonnian literature. It's worth noting that
Empire ships can get big, so it wouldn't be making a pittance.
-The Palace of Misery - a very poor and depressing neighbourhood in Altdorf. On its own, it's worthless, but if we upgrade the place with a major investment of money and/or calling in dwarf favours to improve the place, then we'd have an entire neighbourhood of decent homes and businesses paying us rent forever. It'd also be lifting hundreds of families out of poverty.