In my experience its the grounding that needs beefing up in most cars, not the positive cable. I am sure you will find situations where the lead to power the starter is damaged, but you will find more benefit from upgrading or doubling up the lead from the alt as it has a very aggressive charge curve when you crank up and a heavier wire there makes a big difference.
More grounds help in many ways not just starting. THey help with the radio, throttle response, shifting of a computer controlled automatic, etc. I daisy chain a lot of grounds on my previous vehicles, however my Honda came already like that.
Now starters over time just draw mo and mo power as they age. I was watching Truck U the other day and they tested the starter of a diesel truck with dual batteries. It passed as a working starter, however when they checked the voltage of the 2 good batteries while cranking it dropped to like 9 volts and they said it needed replacing as it was drawing too much.
Now the Honda uses a on/off switch that turns the charging system depending on the voltage of the battery. With a hybrid Honda it uses a dc to dc converter from the pack so your charging system needs takes away from your assisting needs. I found a BIGGER battery to help with the IMA performance and even jumped to a deep cycle. Wow, the u1 deep cycle rocks in regards to IMA performance, charging going up hill, etc.
