Hi Matty, It does seem a bit excessive but the usual on TS's and JTS is 1000 mile per 1 ltr of oil.
Personally I would investigate it further...
Cheap or even free checks you can do:
Oil leaks being the most obvious place to start....
It's difficult to see when a bottom engine cover is on, try removing it for a week and place a large piece of cardboard under the engine block when the car is parked up. It will soon become apparent if there is a minor leak.
Get a "sniff test" done... It shouldn't cost any more than £10 and most garages will do this for you... It involves a hydrometer that measures the presence of any oil or exhaust gases present in the coolant expansion tank thus the possibility of a slight head gasket leak.
I notice you do a lot of shorter trips.... Take the car out for a 100 mile motorway run at constant cruising speed and check the oil before leaving and when you return... Chances are you will have lost nothing! If thats the case then it points to cold engine/ oil consumption issues via valves etc... Pay attention to the temperature guage... It realistically should be up to temperature within 5 miles or five minutes (around the 85 mark) If it is nowhere near on the cruise above and only gets above the 85 in traffic etc. Then that indicates thermostat issues which won't help oil consumption nevermind fuel usage!
A simple test you can do is, when the engine is cold, start her up and place a clean, dry white cloth over the exhaust tail pipe. Be careful not to burn your hand and allow the exhaust gases to breath through the cloth.
You will obviously get carbon soot deposits etc... But see if there is any oily residue on the cloth after a couple of minutes. Usually this will give an indication to valve stem oil seal condition and if the valves themselves are sealing properly.
Nowadays there are companies that offer a 1hr total engine de-carbonising process that bypasses the fuel injection system and uses high quality fuel/ detergents to clean all the carbon out from injectors to exhaust tip... Very good reports about it apparently so if there are tell tale signs above, it isn't a high cost "head off" job anymore.
Perfect timing is the key to all Alfa engines, if its even slightly out it can cause all manner of lumpy running and excessive oil consumption issues so get it double checked to make sure.
My gut feeling would say either of the bottom two suggestions but don't eliminate the pain of minor oil leaks etc just yet... start simple and work through it
Hope this helps mate... let us know what you find