I have only owned a few bits Yamaha gear over the years, but the one I miss most is my SHS-10 'keytar' style FM synth. It was more of a toy and I got it really cheap, but I never really liked keytars as they are not comfortable to play. I gave it to a friend 20 years ago but now I wish I hadn't because it's fairly rare and unique these days. I'd also kill to get another Casio HT-700 as that was my favorite non-pro keyboard/synth from the 80s. Mine died an un-repairable death and I can't find any on the used market that aren't overpriced or broken. Both Casio and Yamaha did some pretty good things with their non-pro lines, but they also had some really terrible keyboards too. Still part of synth history though.