Having done all of this and more, we were disappointed to find that there is still a definite power difference between the two lanes when we tested it before packing up. We're still racking our brains to try to figure out the problem. Our next thoughts are to try some more jumpers on just the outside lane and as I write this, I'm thinking that maybe I should remove the PowerBase and check all its connections. I'm toying with putting back my PowerBase in place of Jafo's own which is currently in use.
Here are some pics I took during the work. We had already put back large sections of track that had been removed when these were taken.
O'Brie and Steve working on the front straight where we joined the straight sections just before and just after the PowerBase (upside down in the pic) with wires soldered to the track rails but with connectors that can be unclipped:

Some of the track pieces that have jumpers, disconnected from their adjoining track pieces:

Tools on the workbench with the all-important liquid refreshment present:

Jumper section marked with a "J". I was going to mark them all but only ended up marking two:

Second marked jumper section:

Sometimes things got complicated:

The new cables joining the front straight with their tiny white connectors add to the existing array of wiring under the PowerBase:
