Been playing around with the 528i some more; I'm getting more and more impressed with the handling. We had a little rain today, and even on wet pavement, I had to slam it around pretty hard (while accelerating) to get even a little bit of slippage (the turns were too narrow to really try gunning it).
And the interior design is definitely sweet. Song names in Japanese can't be displayed (was surprised by that), but the controls are very easy to manage, even without looking. One thing that's a little weird to me is that the cruise control won't stay active when you shut down the engine and turn it back on, but it will still keep the last speed you set. Strange combination.
But I do really love the control layout. I can manage things in it more easily than in my car, which I've now had for seven years and change. The layout is a bit nicer, and the buttons are very well-defined. Including the key fob. After a week, I have no trouble using it without taking it out of my pocket, and I can't do that with my own. It's just a better feel for the buttons (well, mostly; it might also have something to do with me not using mine very often).
Of course, the downside is the cost. The 528i is about 50% more than I paid for mine, and I don't think it's worth that much more. Plus, fun as it is, my TL already has more performance than I need (considerably so, if I'm going to be honest).
Well, I have another year or three to think about it; I don't need a new car now. But I can definitely see the appeal.