I totally agree with old and new about the Miyata's ride quality...my 916 was excellent. Really really stiff for steel. That was a great bike, and I miss her, but I just wasn't riding it at all when I got some other cool stuff. It deserved to be ridden and it ended up funding other stuff. I think it was also important for my fiancee to see I'm capable of getting rid of stuff.
The reason I'd offer lower than what some others have said is because it was stored outdoors and because rx100 really is not what I'd keep on there. 600 tricolor isn't that expensive, but I'd consider that part of the cost of the bike, and rx100 parts aren't going to sell for much to compensate that cost. In general, if the bike can't be ridden...it should go cheap. I think $100 is a decent offer on that piece.