Convertibles are significantly heavier, so be sure you test drive one vs test driving a couple and then getting a vert somewhere else to be sure you still like it. I originally looked at one but the coupe was quite a bit faster.
Would be a bonus if the rear subframe is already reinforced and welded up, that's about a $2500 job, I believe they will all need it eventually. It's even starting to crop up on 330s, time and mileage can cause it as well as abuse, just takes longer.
Vanos hubs have two teeth that can break, I don't think it's super common, mine was inspected at 105k and was perfectly fine.
Depending on mileage, there are a few little things that might need to be done, I've had to do the oil level sensor, another sensor I don't recall, have a new blower motor resistor I haven't got around to installing yet, etc. None of this is stuff is too expensive though. Also, the rear diff needs very specific fluid, about $200 from the dealer, you'll start getting bad noises without it, and oddly lots of shops have a hard time diagnosing this one, fluid fixes it right up.
As far as overall reliability, outside of these issues, I've had mine for about 60k miles and 10-12 years, and it's never been on a tow truck, and haven't done too much other than oil and tires.
Competition package is nice, bigger brakes and a few other things, they were impossible to find when I picked mine up.
I'm thinking about selling my 2002 this spring, but it's not a vert, so that doesn't help you one bit.
