My 2008 E90 has been rock solid. Since its a 323i (which is the same as the older E90 325i) and doesn't have a lot of options, I think it will actually be a good car going forward. No nav, no idrive, no high stressed motor, but the sports package gives me great suspension and 205HP is good enough, I can tell you. 6 speed manual doesn't hurt.
Maybe we'll see a trend in the future where the loaded versions of cars, like the 330 / 335 will decrease MORE in value than the 325 / 323 simply due to complexity and reliability. Interesting thought.
I've seen E90 323i for under $20K, fyi.