Back in the day, the US Turbo Grafx hardware was pretty obscure at best in most parts of the country. Hardcore gamers knew what it was, but the general public didn't have a clue that there was anything out there other than a Genesis or SNES. That being said, I think taking my express on the road with me did as much to market the TG16 hardware as the NEC advertising campaign.
Whenever I traveled, I would take the express on the plane with me. Sitting in the terminal playing Dragon's Curse, Bomberman, or Parasol Stars would draw some attention, but putting on the TV Tuner would draw a crowd! I just loved hearing the oohs and aahs of people that just couldn't believe you could squeeze a color TV in such a small box, and the fact that you could also play games in it was a bonus. The architecture of the handheld was at least 10 years ahead of its time.
NEC shooting for the stars probably contributed to the dissappointing sales in that NEC couldn't really get the price competitive (and wasn't willing to take a huge loss on the hardware like some later companies have done.)
That said, I think NEC shooting for the stars is probably the main reason that the PC-Engine family is the holy grail of collectable consoles these days. In general, collectors love industry firsts, and the PC-Engine family is loaded with firsts. (Yes, you might argue systems like FM Towns Marty and Atari Lynx may have had some firsts of their own, but NEC took it to another level, and did it with everything.) The advanced technology combined with the relative obscurity in the US make it one of those magical combinations for collectors and gamers alike.
If you can afford one, you owe it to yourself to add an Express or GT to your collection! It's still fun as hell to play, and if you have a repaired one, it should last you for years to come.
One other thing, I do agree with Zeta that the LT was the only piece of hardware that trumped the Express back in the day, but back in the day, but that's kinda like comparing a Rolls Royce to the Space Shuttle!
....now if I can only find a boxed Space Shuttle....