The trend for gang thefts in London tailed off a bit when the Police stopped the policy of basically letting the thieves escape for fear of hurting them...and instead, resorted to ramming the little swine off their scooters and into the weeds. Before...they would take off helmets and wear bandana over their faces like wild west bandits. The risk of injury meant the Met left them alone. Saw them quite a few times before....not since!
But the 'serious' bike thief is stealing what can be stolen and moved on rapidly. With the prices of some classics heading into VERY silly money...targetted theft for parts is bound to be an issue.
I have heard of thieves using trackers to 'tag' bikes of value, monitoring their location and seeing where they stop. Then stealing from the storage location. In each case, these were high value modern sportsbikes....but I suspect restored classics will be on the radar.
Casual thieves do target scooters, especially ther smaller end, as lots of kids want them and enough will buy a cheap one with no paperwork and no questions asked. But also, the number of these scoots I see just parked up with no lock, no real security, and even with a crash helmet just stuffed in a top box. Might as well leave the keys in it.....
My Monster chain goes with me if I go out, as well as a disc lock for the other end. At home I now have a garage...and the garage has a ground anchor for me to chain it to. If they get through the gate to access the service road, then through the steel door ( not a flimsy up and over job) they then have to deal with the chain and anchor. While the alarm is going off. Visible deterrents will mean the casual tea-leaf will go elsewhere. Its the best you can do.