I already bought the Bowie albums that I REALLY wanted and I assume that I already have all of his best, so I'm in no hurry to fill in the remaining gaps right away.
Don't be so sure, you might happen to really like The Man Who Sold The World or Black Tie White Noise once you get them. If you ever see Never Let Me Down with the bonus tracks or The Buddha Of Suburbia, just get them, no questions asked. Even if you hate Never Let Me Down, you'll still have two outstanding tracks (When The Wind Blows and Girls) and The Buddha Of Suburbia is just so hard to get (not to mention so good) that you'd be lucky to find a copy even if you're looking for it.