Alright, here's a more clearer point:
Just how far do you want it to go before you're satisfied?
Sure, let's say we add in stuff like canals, and harvesting machines (as in simple machines, non-electrical. I hope the word "machine" hasn't been too distorted in our minds), and maybe let's even put in a husbandry program to teach the farmers how Mendelian genetics work many centuries before Mendel comes around. Ah, but wait! We have to consider that some regions have more than just plain old farming as its industry. Why should agriculture have all the attention! I say that logging, and hunting, and fishing, and mining, and stoneworking, and jewel crafting, all are just as worthy of attention!
Especially for places like mountains. What're you investing in when you make the investment then? The two sqaure meter patch of "farmland" in your estate's backyard? No, I say we invest in a mine!
Now let's make sure our mining is as well thought out as our farming, because we wouldn't like to be too heavily favoring a certain region type, would we? That would unbalance the game! So for mines, we can say we develop better drills, stabler shafts, better freight transport, among other things.
Then for forest regions, we can't forget logging! We need to have better woodcutting devices, better ways of transporting felled trees, methods to prevent insects and disease from killing them, more efficient processing of wood to remove leaves and bark, etc.
Fishing? It's not like farming at all! We need to allow the lord to have the option for better nets, or bigger boats, or more ports.
And you know what? All the aforementioned options should be different choices, with different effects on the production, and all decay at different rates due to different factors.
You probably think this is an extreme illustration, but I consider it a fair treatment of the other potential resource sectors. You can't just go on to invest and improve only agriculture, because the fact is, it's not just agriculture that is being affected when you invest. Food is only half of the picture. The other half has to do with the non-sustenance industries. Treat them with attention too, but how much are you willing to go such that first you would have features that you think are useful, and second, have balance in how much detail you have?
