Do any of these upgrades make a real HP/torque difference on mild, bolt-on street cars or are they just good for helping combustion with forced induction (turbos and nitrous)?

- External coil upgrade with the modified caps
- Capacitive discharge ignitions

 

Not really, honda ignitions are pretty good and there are many high HP setups still utilizing the stock Honda ignition. Some, however, will argue that and MSD setup or something similar will help, but unlikely for just a mild bolt on street car.