(admittedly there are things one can do without too much interaction in ATITD, but I like to have options :).

It's so so so much more efficient to share buildings, and the economic backbone isn't setup well to be able to really specialize unless you've got a semi-socialist setup. So (IMO) the "right" way to play it is in guilds. If I could ignore that, I could probably enjoy playing it single player :-}.