In my mind a car with 50,000 miles on it is just starting to warm up. You shouldn't have to worry much about a car with that mileage. If I was buying, I'd do a plug change, oil and filter change, flush the coolant, new cabin filter and as part of the deal I'd say I'd pay for the parts if the dealer will install them for free. In fact this was part of my bargaining on my last car. The dealer will probably eat the labour.
I bought a 2002 used 330xi - awesome car and you'll love the power. I hope you don't have any speeding tickets right now....lol.