I was given an OmniGo 100 at work once. I liked the form factor OK, but the screen always felt constrained. GEOS was OK, but there just wasn't enough software with the OmniGo to make it work smoothly in a DOS/Windows world. Moving data back and forth, translating it, etc. was a real pain. Also, software development for it was a lot more difficult than it had to be. A lot of stuff that was available on other GEOS platforms wasn't available on the OmniGo.
It basically became a portable Solitaire machine for me. I gave it to some friends, they gave it back. I gave it to a daughter, she gave it to the same friends who had it before, last I heard it was being used as a bedside Solitaire player.
The 120's display was easier to see than the 100's, but otherwise I don't know of much change. As bad as the 300LX was (IMO), the OmniGo was even more useless. A better software package, and better developer support might have changed this, but with the LXs and Journadas I think HP had too many irons in the fire to give the OmniGo the love it needed to be successful.
Nowadays I'd love to have something in this case and with the same keyboard with a good display and a good OS behind it.
I remember there were some folks I knew who were planning on making a sort of open DOS ROM for the OmniGO back when it was still a current system. I have no idea if it actually went anywhere. I don't recall if the OmniGo had its ROM on a board like the 300LX, or if it would have taken swapping a surface mount chip on the board to make the change. The processor would have been a good one for a more or less straight DOS with something like the 200LX's GUI.
As to its present value, I doubt it has much. It's not like it was one of those systems people wanted but couldn't afford, or had and had an attachment to but gave up as technology advanced, like the Psion and 200LX. But I may be wrong. *shrug*
If you can't sell it and don't want it, I'd probably be willing to pay shipping and maybe a few bucks for it to keep it out of the dumpster.