I've had three diesel cars (an 85 Jetta, an 86 Golf, and now a 99.5 Golf TDI,) and like how diesels drive.
I've also replaced an aging 92 Miata with the 99.5 Golf, but still want an open air vehicle. Weird appeals to me, too.
Slow isn't even a big deal - my commute can be done entirely on 35 MPH roads.
So, yeah, kinda toying with the idea of a diesel motorcycle. It'll be something weird, something diesel, something open air, and adequate. It won't happen for a long time (no garage, no welding skills, and I try to keep my number of projects at any one time low,) but I thought I'd join, and look around.