I've owned 7 different BMWs, including a 5 series. They aren't comparable. BMWs offer the best ride/handling balance in the world. They are RWD sport sedans.
The LAX is an near luxury FWD sedan.
While the newer BMWs have softened up quite a bit, and really have gone downhill in the "sport" area, they still far exceed anything a LAX could offer. Acceleration may be close if you compared a 3.6 with the 528, but everywhere else the BMW is far superior.
If you don't care about performance and just want a soft quiet ride, however, the equation is different. The LAX wins in this area.
So, if you want a sporty sedan, I think it's worth it. You get what you pay for. If you want a cushy ride and don't care about handling or the "fun"factor, probably not. One other factor in the value equation is lease vs. buying. If you lease, the difference in payments isn't nearly as high as the $20K sticker. BMW residuals are the best of any maker.