I do not think it is less reliable bc it is a sports car, the e46 is an amazing machine. I have 65K on mine and have not had any problems so far (knock on wood) just make sure you buy from someone who took care of their car, preferably from someone (not anyone young) who lacks track days, so you know it was not driven too hard. This may be obvious, but I think you would be safe by following the following formula:
car's milage / age of car
If this number is below or close to 14,000, you are probably in good shape. If not, there are many aftermarket warranty companies who can provide a piece of mind--EasyCare is a good one, little pricey but you get what you pay for.
Good luck!
