It's not a bad idea to lube them. I guess if they're teflon-lined, it might not be necessary, but Barnett recommends a lube for their teflon-lined cables, and we don't know if the Triumph cables are teflon-lined.
I put a thin film of light grease on the speedo cable once a year, after cleaning it off with a paper towel and some WD40 or paint thinner. I use a lube injector and an aerosol can of "cable lube" on the clutch cable about twice a year, and occasionally on the throttle cables. The throttle cables are more of a chore to get done, but probably don't need the lube as often as the clutch cable.
The speedo cable can be pulled out of the sheath from the bottom. The clutch cable can be loosened at the bottom and then disconnected at the top. The throttle cables have to be undone from the top after opening the housing; pay attention to how they go together to get them back in correctly. And make sure the clutch and throttle are adjusted properly when you put them back together.
A dry teflon lube would probably also be a good choice of lubricant.
