Hi Drowsy.
Just a couple of things; I'm no expert by any means. Just saw your question and hoped I could add to the spreading of ideas this thread is doing such a good job at. Also, I play my campaign at least moderately realistic. Among other things, I don't min/max provinces. Aside from the AI not being able to do it, it's not realistic from a role-play perspective. That being said, on to the meat and potatoes!
I assign each province two tasks - a primary and secondary one. These tasks can be as general as food production or military production, or as specific as Livestock, Culture, Mining, etc. I also, in some ways, integrate what the Roman Republic/Empire actually did gain from holding that specific province. Admittedly it's just from reading Wikipedia articles on the provinces, but it helps me immerse just a tad more.
Italia:
Military/Culture. Obviously, I train both my Legionaries and Auxiliary Legionaries here. It also contain a military training field (The one that adds +Experience, specifically) as well as a temple to Mars. The Culture focus is a great way to make cash, allows you to build one of the Epic Public building Chains, and you can build the Lvl 4 Entertainment centers in minor towns as well (Which, in my opinion, have a great Food/Income ratio. Maybe even TOO good, Dresden

). Round out with Farms in the beginning (representing a rural italia), and then as your empire expands (And subsequently, you can build more farms/herding grounds/fishing ports) I could knock them down and replace them with something else. (Yes, I know it's not cost efficient, but it slows the game down!)
Magna Graecia:
Trade/Farmland. With Ports in 3 towns, this province seems built to send ships 'round the world. So trade is the choice here. Farmland also provides your first real breadbasket province. Picking farmland as a 'specialization' instead of simply 'food production' not only allows you to build cool buildings (Like a granary, or water tank), but also helps me remember that Brundisium will get the Major City Dock Military Chain (Can't remember the name

), and Syracuse will get the other military one - instead of fishing ports. Not only was Brundisium a major military port (Though MUCH later in the empire, if memory serves), it gives you a major naval base of operations on the side where you have a lot of ocean!
Cisalpina:
Slavery/military. I picked slavery to simulate this province being an obvious spot where barbarians as far west as spain, to as far north as the Nervii and Suebi, would funnel into Italia to become slaves or Gladiators. This makes it an ideal industrial province, that is often the 2nd or 3rd highest income province (Rome being 1st, always). The Military specialization usually includes building a military training field (I have the mod that enables building it in minor towns. This specific choice is combat posts) as well as an auxiliary barracks. This breeds some fierce barbarians who are romanized! Patavium usually gets a mine (A shout out to the original Rome total war, I could swear you could build a gold mine there). Genua will get the Stone quarry. More Industry income, plus increase in % earned from slaves? Yes Please!
Corsica Et Sardinia: Food/Commerce. Admittedly, the isles never are a terribly high priority for me. I capture them (Or try to) near their historical conquering date, so usually my focus is on mainland province development. Historically though, it was a major grain supply for Caesar. So it gets farms, and fishing ports. Later in game, Karalis willy usually have it's fisherman's wharf converted to a trade port.
You might've been able to tell, but this is just one mini "Group" in a larger layout of the Roman Empire. I hope this wasn't a bore to read... I'd happy to share more if anyone had interest!