Yes, there does "unfortunately" seem to be a glut of MWT's for sale currently which is not helping resale value.... I think there may be several reasons?
The Transporter is very probably at its best with the EML mesh plate and there has been some longevity issues for a few folks.... me included. The EML seems to be like a racehorse.... superb performance when in a perfect environment. If not perfect (and its very particular) there are problems. Dan has gone out of his way to try and accommodate the finickiness of the EML with multiple mods to the Transporter. Apart from capacitance and transformer impedance matching, it seems a major issue for longevity is filament voltage.... and the big EML seems happier with it significantly lower than most other tubes need in the Transporter. If running an EML, voltage checks should definitely be done to preserve it.... talk to Dan.
I think this desiring an EML for best performance, but not wanting to deal with the longevity issues has put a few folks off...? The other issue may be the recent popularity of high performance stand alone DAC's (without finicky tubes) and computer based servers and simplification of the music system...? As to questions of typical modern product life cycles.... who cares, its a great totally reliable unit that works fabulously.... and we all still search for NOS tubes that aren't made anymore don't we?
Me personally, I'm sticking with the Transporter and have gone out of my way to make it EML friendly.... no, I"m not on my first EML and so have some experience. The good news is that Black Treasures have reportedly a long life.... we'll see?
I love my Transporter because its so flexible. I use its as a central switching hub for multiple inputs and all sources benefit from the excellent tube output DAC. It's also my volume control as my amp doesn't have a remote. The ability to access CD's (on my computer hard drive), play DVD's and also listen to internet radio all from one unit is great for me. The latest great sounding stand-alone DAC's don't offer this much flexibility and so don't currently work for me. That's my story and I'm sticking to it.... for now anyway.
I appreciate that technology moves on and the latest and greatest DAC may sound a little better.... but how...? I believe its MUCH more important to get that little bit of "magic" in your system. That magic that won't let you leave a room until a song finishes... that magic that stops all conversation in a room when you put a song on.... that magic that won't leave your foot alone with a favorite song. That magic comes from synergy.... not always the latest and greatest.
Cheers