I've owned 2 (nearly) of the cars on your list...
A 2001 520iT, which is a European version of the US cars... Still has an M54 engine, just smaller and underpowered. It had a 5-speed manual. We bought it for $800, well neglected, and all-in it owed us ~$2500, which included $400 in new tires. I DIY'd everything. It was very easy to work on. When we bought it, I baselined the car by replacing all of the standard fail points on the M54, which included oil gaskets and the entire cooling system with radiator. Aftermarket parts are inexpensive and it made it drop dead reliable for the year we owned it... I don't see value in OEM parts on an $800 car. It was a rust-bucket and failed inspection after the year, so I sold it rather than fix it. The guy that bought it patched up the holes and the car lives on today. Rust won't be an issue in CA. So I would vote for one. This car had 270+k kilometers.
We replaced it with a 2005 Volvo V70, which is the P2 platform, so a little older than you are looking at. Apparently, these are considered throwaway cars, which was great for me because we got it for $1300 with 155000 miles. It is rust free and still looks fairly new. The interior is in fantastic shape and the leather is much nicer than what we had in the BMW. It is a different animal than the Bimmer. It is not as much fun to drive (it is squishier and has a slushbox) but it is a 2.5T with a low pressure turbo and has plenty of power. It is also easy to work on... perhaps easier than the BMW. It has some weak points but parts are similarly inexpensive. Again, with a car this cheap, I don't see value in OEM parts. With it, I had to rebuild the PCV system because it was plugged and shortly after we bought the car caused it to quit idling. $200-$300 parts and a half day of DIY (with some tire kicking) and it was good to go again. We also had a coilpack go bad. Currently, I'm seeing excessive oil coming from the charge air pipe from the turbo, so I think a rebuild is in order. I say rebuild because it sounds quiet and still produces plently of power, so I'm not expecting major damage or wear on the turbine (I could be wrong). It will be fixed shortly. I realize this isn't a P3 like you mentioned but they are similar cars and are probably more evolutionary than revolutionary.
Both can swallow a sofa with the tailgate closed. Ask me how I know
