I have owned a few basses in the $600-$2000 range and one in the $2000-$4000 range. My No. 1 bass, and by far my favorite, cost less than $1,000.00, so I don't think I'm particularly biased towards uber-expensive instruments.
However, the sole bass I've purchased in the $2000-$4000 range (a Zon) is far and away the best constructed instrument I have ever owned. The level of playability far exceeds any other instrument I've put my hands on, counting both basses and guitars. From the perspective of craftsmanship and finish, everything about it is flawless.
In addition to that, getting into the higher price range opens up custom options that generally aren't available otherwise. My expensive bass is literally unique, as I requested a combination of changes from the builder that ultimately required them to redesign the body for this particular model and build mine as a one-off. The reason this matters to me is that my specific purposes on buying this bass was to get a high quality gigging instrument that was as light, ergonomic, and easy to play as possible to help me address some injury issues, and this simply would not have been possible with an "off the rack" instrument.