New or used cartridge

I'm as guilty-maybe more than some, about not reading the initial question thoroughly, or posting "my" response before reading others. My Urushi Black is in very good condition. It doesn't need to be serviced. Just thought I would consider my options, as far as moving up the food chain.   I've seen where some retailers offer a trade in allowance of as much as 25%, but their prices are already inflated, so that doesn't mean much. May go up to a Jade Platinum. I need to go online, to get a description of the different sounds of each. If any of u can describe the different sounds of the upper line of Koetsu's, I will appreciate your input. 

@terry9 
They're just a deputy service that facilitates the transfer of Japanese goods. They would route your cartridge directly to Koetsu Japan (which is the only place to receive a genuine rebuild) on your behalf, just as if you were a Koetsu owner living in Japan. I haven't yet used EIFL myself, but it looks like a viable option, and I've used deputy services from Japan in the past for purchasing other goods (often of quite significant value).

@handymann
Yeah, trade-in won’t get you much unless you can use it as a bargaining chip for a dealer that’s willing to cut into his margin. Probably better off selling the Urushi yourself.

The stone Koetsus are all wonderful, though unfortunately I haven’t heard an Urushi. The differences between Onyx, Jade, and Coralstone are all relatively subtle. They each have better (more powerful and clean) bass response than the RSP. The Onyx is a pretty excellent all-rounder. The Coralstone is a slight bit more warm, organic, and fleshy sounding. It is probably the best sounding, overall, by a small amount. But they’re all great and give the full dose of Koetsu magic. Don’t stress too much over the stone differences. I highly recommend any of them!

Do give consideration to the amplification needs of a 0.3mV output platinum. The Bob's Devices Sky SUT's make for an extremely synergistic pairing with any stone Koetsus, for a very reasonable price.

My KRSP with diamond cantilever has a subtle but unique smoothness in the mid to high frequencies. I attribute this to the fact that the stylus and the cantilever are one piece of diamond - but that's what I was expecting, so maybe I'm fooling myself. Worth $4000? Don't know. But I'd like to compare it to a stone body on my air-bearings.

@mulveling 

I've also heard that Koetsu will not touch a cartridge that's been worked on by any 3rd party.

Not only Koetsu, but almost every respected manufacturer will not touch the cartridge if it was refurbished by somebody else before.