Well, it's certainly interesting to hear some different opinions on this. I myself was never interested in reading the Liveship books for the simple fact that live ships never interested me. In fact, after inhaling the Farseer and Tawny Man trilogies, I was very disappointed to learn that I would have nothing else to read from Robin Hobb.
I loved the plots of the Farseers and Tawny Man trilogies, but most of all, I loved her characterizations. I think that's Hobb's strong suit. I've never seen fantasy characters approached with such depth and realism. Fitz was fleshed out, hangups and all. Hobb took such time to understand her character that he seemed
real, even more so in Tawny Man, where action took a backseat to character interaction- I understand if not everybody liked that as much as me.
That said, I understood that trilogy perfectly without Liveships, so unless you want to read more on the Fool, I think you're fine without. I was hoping for a different ending myself, but Hobb pulled off that ending beautifully, so I can't complain. As for useless characters, I couldn't see that there were any in the two Farseer trilogies, especially as characterization was so important. I always considered Starling a mirror to Fitz's loneliness and isolation. That was her purpose, to highlight that for the reader.