You definitely wouldn't buy Feodum for points in its own right, but if you had a few in deck and bought Farmlands that would help keep your money density up for the other cheap ones (and that would increase your density better than Harem, and maybe even Nobles depending on how bloated your deck already is).
OK, I had not thought about Farmland giving Feodum->Harem + 3 Silver. There's probably a strong argument for that. The problem is getting the $6 consistently
before this starts giving you a Silver flood.