Until the LCD failed on my LogicDart, it was probably my most used piece of test gear. I found it really useful when doing board bring-up or firmware dev, and was really handy to have for any low voltage work when visiting client sites. For I2C or SPI or other protocol decode it doesn't come close to a Saleae or MSO, but it helped me diagnose a huge number of HW & FW issues over the years.
I miss my LogicDart
The LCD is the same one as that used in an HP48. Prices on those have risen somewhat but they're still pretty common, and some even have the higher contrast black LCD. Maybe you could repair it with HP48 parts. Also, I thiink the HP48s tend to fail with zebra-strip connection problems so maybe the same techniques would repair your Dart.
I always wanted one, just because they seemed to address things that I worked on. But you're the first person I've seen finding them really useful so I haven't been willing to pay the going rate even on the rare occasions that I've seen one for sale.
It makes me wonder, though, if it's a concept that could be revisited. The Saleae analyser, as you say, is absolutely wonderful. That's a combination of a nice bit of mechanical engineering and some superb software. The later analog versions take that to another level. I don't know if it would be so good as a handheld or a phone accessory but .. maybe. The point is, it's relatively low tech (first version was very little more than an FX2 board) but has been designed and refined by someone who really knew what they wanted.
Maybe a thread somewhere else on designing a kick-ass logic probe ? A Flipper-zero for wired signals ?