My own personal experience regarding the importance of the Adam historically, is that it had almost no impact at all. It got almost no magazine and 3rd parties support compared to its contemporaries for example. And no one tried to compete with it, at least not to the extent of the Apple II/C64/Atari feud. It was also, for me, an ill conceived machine with its dependency on its printer for power and tape drive that could be erased by turning the machine off with a tape in it.
It was just another z80 based computer lost in the sea of 6502 based home computers in its market. It may have had a better chance if it had launched and concentrated on the european/asian home market where the z80 was popular and many were developing on it.
It was literally on the market for just a little over a year. Considering how vanishingly short that was, it got quite a bit of support and coverage.
Besides the low end elephant in the room, the C-64, which sucked the life out of all comers in that space, Coleco obviously botched the Adam's launch both with fluctuating prices and their lack of quality control. They really bit off more than they could handle. With that said, it's really a pretty nice machine all things considered, particularly once you deprecate the tapes in favor of disks and you utilize some of the bug-fixed ROM chips.