I'm having one built right now.
I feel a little biased because I'm good friends with the builder, so take my review with a grain of salt, but here it is.
Nash Guitars are killer in every aspect. I have never heard a bass sit so well in a mix, whether it was live or in the studio.
The fretwork is second to none.
Amazing set-ups (for those who have to ship their basses or they are in other parts of the states, you really have to get a feel for how Nash Guitars really does their setups, they're incredible!)
The neck pockets are nice and tight, which leads to them being incredibly resonant. Even unplugged, you get that huge piano like tone.
As for the "parts bass" argument and if the basses are worth what you're paying for. Absolutely. If Bill made his own bodies and necks, you'd probably be paying double the price for the same product. So getting a quality body and neck from a reputable dealer I think makes a whole lot of sense.
In short, I think they're worth every penny, but ultimately, it's really just up to how you like your bass. IMHO, a Nash is the quintessential definition of bass: solid.
Someone's review for an Aguilar DB750 summed it up perfectly, but I'll change it to work with this. "This bass was not made to reinvent the wheel, just reproduce it flawlessly". It's so true!