Seems like a reasonable price - but I haven't looked at used-car prices. The 335d's resale priced dropped very quickly, as everyone knew that they had been bought for cheap with the 3500-4500 dollar off special price. You might compare it's price with similarly equipped 335i's; but I don't know if you add or subtract $2,000 after that (that was the premium for a new 335d over a 335i.)
Other than many little problems with the SCR system, there appears to be nothing notorious with the diesels. Note that there was a 3-part recall to fix some common EGR/SCR/DPF problems around 6 months ago; be sure it's been done.