I've managed to keep my bike locked up outside OVERNIGHT in San Francisco (Washington & Polk St.) for a year now. How I did it? The short version: one very good lock (Viro Euromonolith + Peewag security chain, $175), a second good lock (kryptonite, $90), and an okay lock (Abus, to keep them from stealing the basket, $60).
I've also had 3 bikes stolen, the rear wheel stolen, the basket stolen, the front brake stolen, the seat stolen, but now with all the locks there is much less stealing.
The bike was around $700-$800 new (I bought it used for $500). It's a Public bike, and their closest current model is the PUBLIC M7i, which retails for $799.
It's a target, but it's certainly not a "juicy" target like, say, a $3k mountain bike.
The bike thieves continue to steal the small stuff, notably the rubber attachments which hold my bike lights, but haven't been able to steal the big stuff (frame, wheels, basket, seat) in a long time.
One of the strangest things that was stolen is the yellow electrician's tape I used to "dog" my seat with—they painstakingly peeled off the tape, but left the seat.
A stolen front v brake / rim brake? They're going to trade it along with a few other choice bike parts they've collected for $15 worth of meth, crack or synthetic opiates.
I've also had 3 bikes stolen, the rear wheel stolen, the basket stolen, the front brake stolen, the seat stolen, but now with all the locks there is much less stealing.