My 328Ci's lease is up in 5 months about so I will be looking for a new car soon as well. My brother however just picked up his new 2004 545i Silver Gray last week. I drove it home for him, since that's a little tradition we started with my car. Anyway hes got the sports, luxury, and sound packages and I have to say the car is great in every way. There is plenty of power, and although he still hasnt even begun to test it (about 600 miles into his 1200-1500 mile breakin) you certainly wont be lacking jn the speedy acceleration department.
The handling is unbelievable especially with the active steering, which sounded bad on paper when I first heard about it, but now that I've driven it I love it. It's only a single turn in either direction of the steering wheel, as opposed to the 1.5 turns we currently have to do in our 3-series, allows for much sportier driving. Also the car feels absolutely amazing on the road, very nice gear switches, amazing sound, the clutch feels like it wants to rip out every second, car will definitely be fun for a few years to come.
With the 530 obviously you get less power but everything else should still drive the same, I would recommend you test drive the sports package version and see how it suits you. Its certainly a very roomy and comfortable ride, and I havent found anything to bitch about it yet. Except maybe that I want one also.