Oh there was a nice sit down set up on Craig's List today, still no room for it!
My modern Bernina 820 has a huge throat and I can happily and easily do a twin size -- and if it was in a table I'd consider a queen, but still not the same as the long arm. Unfortunately, Bernie needs a servicing and I am just not going back to my old vintage machine.
I think there is just a basic difference between moving the machine which I do better than moving the quilt, which many people do better than I do.
Edit/PS: You can have a long arm set up for chair height, one of my friends is set up that way. She says you quickly get used to involving your feet in the process but she likes to have really loud music on while quilting!