Matt: um........ I dunno
Well, let's just remind ourselves that this is, afterall, the developers' board, and not suggestions board. I think this stuff should be copied and pasted into the suggestions forums. I personally have a lot to say.....I will post my ideas here

What I have heard and suggested myself so far is, delightfully, on track in my opinion
I think by having an animal farm merged into a crops farm isn't very popular, since animals, living happily oinking/moooooing/bahhhhhing (or maybe the sheep are not so happy......bahhhh) on the pasture, once they see something just a bit more tasty than the plain old green grass, e.g. corn and barley and the rest, then they'll go and eat those. That is why i think there should be a separation- walls are not enough, we all know that cows can jump over the moon, so why would anybody then think they can't jump over a 5 foot brick wall for munching the corn?
About building upgrades. VERY good. I like that. esp. for factories and their heavy machinery inside, it makes perfect sense. I'd also like to see different levels of factory expansion- esp. in working efficiency, the building's general sheer size when upgraded....half operational, and half in scaffolding.
I'd LOVE to see factories adding expansion parts on, functional part in the origin square, and then expanding from the square into maybe a 2x3 square big building, to a 4x3 square big building. Costs are to be VERY expensive, but it will booost working efficiency like hell.
The complication: if there is a road or another building nearby owned by someone else, how can you expand!?!??! Well, the expanding owner will have to communicate with the owner of the nearby building: either buy it then demolish it, or just stare at your unupgraded factory to rust
bah, ideas come with more ideas:
land ownership
When someone builds a building, they must first buy the land- i.e. one square for the very primitive factory...... before they can build the factory itself. For expansion, more land is required, so the owner must buy the land around the one sqaure before any new extensions are to be added to the existing building. similarly, land must be owned by a farmer before he/she can use it as farmland. This will clearly show the ownership of land on the world (island) and will contribute to the clearness of building expansion space, competition for land and the operations of various other factors.
LAND IS EXPENSIVE. the nearer to a town plinth, assuming that is where all the people visit all the time, the land is more expensive, because sales of products are expected to be high. On the other hand, land in the open country is cheap, ideal for farming needs. They are buying just a piece of grass where their corn/cows/sheep/barley/super-Mit-lookalike-monkey-aliens can grow and be sold. However VAST amounts of it is required to achieve the effect of an upgrade in a factory.
I conclude by saying: "MAAAAKE THE WORLDS BIGGERR! IF farms are to be expandable, then we need a great countryside, which, really would make the islands more realisitc- it would actually take TIME, at least a few minutes, to get from London to Cambridge, or in island distance, about 10 widths/lengths of the square map. THAT THEN leads to motorways, but if I continued, i'd contradict myself- it's not a conclusion then, is it?!?!