I have seen where people have discussed throttle linkage wear. Does this refer to the intersection points where the throttle linkage penetrates the SU carbs and any associated vaccum leaks at those points?

That's a possibility, but usually the problems are in the plastic sockets where the linkage can be taken apart. A lot of times it is just accumulated grit and grime that causes the problems. It's a good idea to lube them and take apart the bell crank assembly where the linkage comes out of the firewall and lube the post on that. It comes apart real easy, just remove the snap ring and pop off the rods and lift it off.