So would you say a big, late model bike is actually safer to leave around than a smaller, older model?

It is only my opinion. But, for example there are 1000s of little scooters running about in Russia ridden by kids and heap of shops selling these. I figure someone riding around on KTM is bound to attract the attention of the cops sooner or later and as such the problems around stealing and keeping one for yourself or selling is worth the effort, whereas scooters run in and about the place everywhere, even small villages often with no number plates. Succesfully stealing a scooter is unlikely to see you caught.

The guys that killed the Japanese tourist near Chita were caught after the bike was discovered in the village and then someone went and found the guy dead.

That said when leaving the bike I always take off the easy to remove stuff, GPS, tank bag and if for a long while panniers.